I think after Jesse and Celine finished laughing about him missing the plane, he did end up going to the airport to get on the plane. They did exchange phone numbers and information this time. They do stay in touch and really want to be together, but Jesse is unwilling to leave his wife because of Hank. Eventually, Jesse’ s wife grows tried of him spending so much time talking to this woman from France and she ends up having an affair and leaving him. But by this time Celine is pregnant and engaged to another man in France.
Apparently, there is going to be a third movie in the series, but Linklater has signed over the rights to Michael Bay.
What happens is, Jessie stays and Celine is about to declare her undying love for him. She caresses his face and notices there’s something weird about where his temple connects with his hairline. Suddenly Jessie rips off his humanoid face mask to reveal that he is actually a reconniassance scout from a hostile alien species. Turns out, he’s been using Celine to learn about earth customs, language and mating rituals, prior to a full-scale invasion of the Earth.
Having no further use for Celine, Jessie Alien attempts to slay her with a really cool laser weapon gizmo. Celine fights back and well-choreographed mayhem ensues. They grapple and punch each other a lot. In fact, they totally wreck Celine’s apartment and several fires break out for not entirely clear reasons. The pair of them, locked in a vicious fight to the death, do the usual stuff like tumbling through pulverised walls and hurling one another through plate glass windows in slow motion. Their epic struggle spills out into the street and lots of innocent bystanders get zapped to ashes by this futuristic laser gizmo. The heavy metal soundtrack is pretty good at this point.
After this massive fight, Celine somehow manages to escape. She flees and seeks to alert the authorities, but they don’t believe her. Frustrated, she decides to try and get the message out through her connections with eco-warriers and concerned environmentalists. The main group she contacts are a sort of eco-survival commune that live in some cool-looking underground lair. They are all either totally foxy supermodels with attitude, or tough guys with snarly faces and a very rigorous workout regime.
Meanwhile, in the aftermath of his street brawl with Celine, Jessie Alien morphs into his normal, alien form. He is sort of like Predator but smoother, with T-1000 metallic skin and a sort of transluscent sheen that looks like it was quite expensive and time-consuming to achieve. This will make for an excellent article in magazines devoted to special FX. He sets up an alert beacon gizmo to summon fighter squadrons from his species. These squadrons, it turns out, have been in orbit around Earth for nine years, but in ‘cloaked’ form. The way they de-cloak is another really cool FX shot.
The alien fighter squadrons descend and blast Vienna and Paris to rubble (because this is where Jessie placed the first two homing beacons). The military top brass realise that they should have listened to Celine after all. But is it too late? They kick into top gear and press large red buttons that have words like ‘Combat alert’ and ‘Initiate Launch Sequence’ written on them.
Next is a cool montage of military guys shouting orders at one another and big fighter planes launching into the air and stuff like that. The soundtrack is full of people exchanging sound bites over comms systems using what sounds like fairly authentic jargon. These sequences are interspersed with a clips of TV news anchors stating that the Earth is being invaded but the military has launched a counter offensive (just in case we didn’t get it).
The next half hour is pretty much just fantastic battle sequences, with just about everything, everywhere being blown up. The military look like they are getting the upper hand, but then the Mother Ship arrives, which is, like, totally massive and impregnable, and it looks like it’s Say Goodnight Gracie for Earth.
However, Celine and her cronies have discovered that while the aliens can defeat our military machines and weapons of war, they have a fatal weakness ! Yeah, I know - who would have guessed?! It turns out that sweetly sung love songs are fatal to the alien nervous system. (This is inconsistent with the ‘waltz’ sequence at the end of ‘Sunset’, but since when has internal consistency mattered in a blockbuster movie?). Celine and her eco-warrier friends, armed only with guitars and a bunch of Celine’s songs, advance upon the alien armies and manage to silence them, eventually causing all the alien ships to self-destruct in massive fireballs that look pretty freakin’ spectacular.
However, while this may take care of the alien ships that have been zapping Earth, it doesn’t affect the Mother Ship because it’s out of range or something. This is a problem, because the Mother Ship is preparing to fire the really big zap gun that will annihilate Earth, and we know this because there’s a detailed countdown sequence with big red number displays showing how long we’ve got left.
It seems that Earth has no chance… but Celine uses the internet to hack into the Mother Ship’s systems (this part is a bit vague) and uploads one of her songs. Sure enough, this causes massive damage to the Mother Ship, and most of the alien crew are seen to writhe in pain and then dissolve in a really cool morphing sort of way. The countdown to the launch of the big zap gun thing stops with about 3 seconds to go. However, it becomes clear that while the Mother Ship may have sustained a lot of highly photogenic damage, it is still just about operational.
In a touching climactic scene, Celine tracks down Jessie Alien and they face off. Celine’s concerted strumming on her battered old acoustic takes Jessie to the brink of death. But then Celine realises she cannot actualy bring herself to finish him off, even though she knows he’s like a bad evil alien dude who would have, like, totally wasted the entire human race given a chance. They have some sort of touching final exchange where Celine hammers home the point about ‘love conquers all’, just in case we didn’t get it.
Jessie Alien triggers some sort of personal teleport device (a capability not previously acknowledged anywhere in the plot thus far), escapes to the Mother Ship, and leaves. However, his last words indicate that he will be back in nine years.
Celine has found time in all this to get romantically involved with the main Hot Hunk O’beefcake from the underground eco-commune, who now barges in and sort of ‘rescues’ her. They wander off together into the sunset amid rubble and smoky ruins while the camera pulls back and up, up, up, indicating that we’re in for a ten second hold on a beautiful sunset before a rapid cut to black, the start of the credits and a heavy metal track that is on the tie-in album.
And that’s what happens.
Mr. SaharaTea would have been much more interested in that movie, ianzin. 
I think it was pretty well implied that Jesse would miss his plane and something would happen between him and Celine. He would have gone back to his wife for a few more years out of guilt, but the marriage would ultimately fail anyway. By that time Celine would have married and had a child too.
The timing would never be right. And they have to live the rest of their lives knowing it might have been different if they had only exchanged phone numbers the first time around. Morons.
It is now two years later. Jesse and Celine meet in a street in Vienna. The camera has followed them separately as each has stopped at one or two of the places in the first film on their way to their meeting.
They meet. They are in front of a court house, surrounded by legal types and excited media. They don’t speek to each other.
Throughout the film it is told how Jesse stayed in Paris with Celine for a few days. As the passion settled and they tried to work out how to spend their lives together, Jesse made it clear he couldn’t live anywhere but America. He was willing to leave his wife, but not to live in a country where he couldn’t have regular access to his son. Celine would not live in America - and said so in a few more rants such as the one in Before Sunset.
Jesse returned to America to leave his wife but be near his son. He couldn’t manage to write another book - he didn’t have another story to tell like the one he had already written. Celine found every relationship dissoved because none could live up to the heights of that one night. She took her revenge by writing her own version of that one night in Vienna to try and destroy her memories - a way of purging the images. She claimed Jesse’s best seller was all lies. She had left the train with him, true, but soon discovered he was not what he had seemed. He had raped her. There never was any arrangement to meet in six months. Evidence is provided that Jesse had not returned as he had told Celine. That had been a lie.
The book was a huge success - women’s groups the world over championed it as testimony to men’s animalistic and devious ways to get the only thing they ever want from a beautiful, naive young French girl. Celine was portrayed as a noble and innocent worker for the good of the environment, Jesse as a sick male who had capitalised on his conquest in his book written to torture his victim even further. The sudden fame and pressure of the women’s groups meant that Jesse was charged with rape. He has lost all access to his son The trial involved legal jurastictions of three countries, and it is here the film opens and flashbacks get us to this point. Now the battle begins.
Will Jesse’s name be cleared? Will Celine melt at the sight of him and regret all the evil she has done? Is there any evidence to support either version of events which can be presented to the jury? Is there any way these two lovers can be reconciled? The third film will reveal all!