Isis
Rhiannon
Thor
Venus
and a few hundred thousands of others I do not know. or be redundant to those listed.
At their peaks, people built temples in their honor, prayed to them, and generally thought they were immortal.
Hindu probably holds the record for “Number of gods believed to exist” - something like 337.
Do Gods die when their last believer forsakes them?
(yes, I DO remember the ST-OS episode) 
The Norse gods are definitely not immortal even if they still do have believers. They die in the battles of Ragnarök. It may not be all the gods, but definitely the major ones Odin, Thor, Týr, Freyr, Heimdallr, and Loki.
In Greek Mythology, I believe Chronos (Roman Saturn) was killed by his son Zeus (Roman Jupiter).
Balder died…
(There are some minor myths where he comes back again, but I believe the “official” tale is that he dies, period, the end, wah.)
And in Ragnarok, a whole bunch of them are destined to die! (Like, all of them?)
ETA: Ninja’d! Also, I don’t think Chonos died; wasn’t he just mutilated? Or am I confusing him with Ouranos?
Robyn Hitchcock’s song, Mexican God, compares the lingering memory of a past lover with the fading of an ancient religion.
> Time will destroy you like a Mexican god
> At least when I die, your memory will too
Yeah… I’ve been there…
The graveyard of the Gods is in the skulls of dead believers.
My understanding is that in monotheistic and semi-monotheistic traditions, where you have one god who was the creator of all, that god tends to be immortal. Get into any where you have a range of gods with no clearly defined creator and all bets are off.
The idea that a god’s power is directly related to the number of believers is a key point in several of Pratchett’s Discworld books. When the last believer is gone, so is the god. (But archaeological/documentary evidence might spark a return of belief and thus a return of the god.)
I think it’s time for the return of the Ugaritic/Levantine god El. His son Yaw has gone all monotheistic.
In most polytheistic systems, the gods have eternal youth, but are not indestructible. Kronus killed Ouranos, Zeus killed Kronus; Ra died and became the sun-god in the afterlife. Osiris died and became the judge of the dead in the afterlife.
The Norse gods did not even have eternal youth. The depended on a magic apple tree, tended by the goddess Idunn, to stay young.
Some Buddhist sects believe that there are multiple worlds. Some of these worlds are heavens, populated by gods. Others are Hells, populated by devils. If you do good deeds, you might get reincarnated as a god, and spend a few centuries enjoying the heaven. If you do bad deeds, you might get reincarnated as a devil, and spend a few centuries enduring the hell. The gods and devils may have vast power, but they can still die, and then they will have to start yet another cycle.
In some Hindu stories, gods and devils are perpetually reincarnating. In one incarnation, A will kill B. In the next incarnation, B will kill A. There is one story where a god tells a man, “We have both lived countless lives. There is only one difference between us: I remember my past lives; you do not.”
The Shinto religion holds that there are a vast number of kami, although most of them are what we’d probably call “spirits” rather than “gods” in English. There are said to be eight million kami, although this isn’t intended literally, it’s just an expression that means a huge number.
in the court of the Emperor of Heaven (Chinese), you have the Elixir of Immortality, but you also have the Peaches of Immortality.
(from the Wiki page below)
Journey to the West
It is a major item featured within the popular fantasy novel Journey to the West. The first time in which these immortal peaches were seen had been within heaven when Sun Wukong had been stationed as the Protector of the Peaches. As the Protector, Sun quickly realized the legendary effects of the immortal peaches if they were to be consumed – over 3,000 years of life after the consumption of a single peach – and acted quickly as to consume one. However, he ended up running into many fragments of trouble such as a certain queen that was planning on holding a peach banquet for many members of Heaven. He manages to make himself very small and hide within a sacred peach. Later on within the series, he would have another chance to eat an immortal fruit – in which would be his second time. A certain 1,000-foot-tall (300 m) tree was stationed behind a monastery run by a Taoist master and his disciples- in which the master had been gone. The tree bore 30 of the legendary Man-fruit(fruits that looked just like a new born, complete with sense organs) once every 10,000 years. The man-fruits would grant 360 years of life to one who merely smelled them and 47,000 years of life to one who consumed them. After this point within the novel, these Immortal Peaches would never be seen again.
Baldr is one of the gods who comes back after Ragnarok (also including his brother Höðr, and Thor’s sons Móði and Magni). Since it’s implied that Baldr essentially becomes the new chief of the gods, the Christians seem to have deliberately syncreted Baldr and Jesus when converting Germanic peoples.
I’m not at all up on this stuff, but I’ve heard people argue that this “happy ending” was tacked on to the myth cycle by lesser, later writers. (I do not know at all if this is a fair or valid claim. The only actual cite I have is an essay by Fritz Leiber…and I can’t find that right now!)
(I want to make a really unfair comparison to Ovid and Virgil tacking stuff on to the end of the great Greek myths…except that Ovid and Virgil were GREAT writers!)
The stuff about Baldr’s return is in the Völuspa portion of the Poetic Eddas, which is one of our main sources for Norse mythology. So, probably not tacked on later by others.
Greek myths, I think, suffer from multiple not-quite-contradictory story traditions being merged together. And then later generations revising how they regarded the whole thing. Egyptian mythology had the same problem - there are at least two entirely different origin cycles smushed together in there, and Ra ended up syncreted with just about everyone; it’s a bit of a muddle.
The Romans outright stole from the Greeks, and syncreted in their own gods on top of it. I don’t think Ovid and Virgil were tacking stuff on to Greek myths, but on to Roman myths they’d stolen from the Greeks. I have no idea if that would make their additions more or less legitimate, but probably makes the OP’s question unanswerable. Too many contradictory versions of gods people think are the same.
Lightray: Super! Thanks!
And even among the Greeks, there are contradictions. For instance (if memory serves, and it very well may not) Hesiod put Eileithyia in the list of the Olympians, but other lists do not. It’s all wonderfully tangled.
(Hesiod’s vast “family tree” of gods, titans, giants, and lots and lots of monsters is a true joy to study!)
Given that there is no proof that gods have ever existed, the question is moot.
And yet, other posters in the thread have been able to provide responsive answers to the OP. There is no cause for threadshitting here. Don’t repeat this.