Assuming the US leaves NATO completely then its up to them to let the Ukraine or anybody else to join NATO. This might actually be a good thing for Europe, as they are not poor or by any means a third rate power.
Not just Peter Zeihan (and I share your skepticism of his broadly sweeping claims with a paucity of citation); the Russians have been importing foreign technology and expertise since before the fall of the Soviet Union to sustain their petroleum industry and are highly dependent upon this to keep it running it because their ability to internally develop expertise has dropped sharply in the last few decades as the oligarchs running these industries have not invested and developed their interests. And even of the petroleum they can extract most of it has to be sold as crude oil at pennies on the dollar because Russia lacks modern or expansive refinery capabilities.
Regardless, the demographics of Russia are plain; even the official statistics show them as being well below replacement levels, and independent analysis shows Russia to be at the absolutely bottom in terms of negative population growth. Putin’s incursion into Ukraine was plainly an effort to demonstrate that this is not a problem (and in my opinion mostly to bolster up his appearance of strength and appeal to national pride within Russia), and the catastrophic failures of what was supposed to be a couple weeks of operation to capture Kyiv and install a puppet government made a mockery of that.
This is assuming that the alliance holds together, which is not at all assured. Depending upon political developments in Germany, France, Turkey, Poland, et cetera, the fractious nationalism that brought Europe into the First World War has a real potential to be realized yet again. This still won’t make Russia more powerful or ultimately sustainable but it will be relatively less weak compared to a Europe unified under NATO. The United States has always sustained NATO (mostly for its own interests, which post-WWII included a stable Europe to buy agricultural goods and oppose Soviet expansionism, and post-Cold War as an investment hub and to maintain American global hegemony) and because it was not of Europe it could mediate intra-continental political disputes and if necessary throw its economic might into suppressing discontent, but now that the US is signaling a desire to turn their back on the alliance it is really the question of who will step up and take the reigns to ensure that there isn’t a leadership vacuum or lack of direction. France? Germany? Poland? Will other NATO members all fall in line behind one of them? I don’t know, and I don’t think anyone else can provide assurance that NATO will endure without an American overwatch.
Stranger
Is it out of the question that the US would even provide material support to Russia?
I mean, it’s pretty clear that Russia has successfully captured RW media in the US, and it’s also pretty clear that whatever memes people in the MAGAverse believe now become policy. The flowchart of propaganda to policy has only two boxes.
What guardrail prevents even that from happening?
Not at all. They likely will.
My understanding was Oceania has always been at war with Eurasia.
“Drill, baby, drill!” isn’t just applicable to the Arctic Wildlife Refuge. If we can get some of that sweet Siberian oil in exchange for advanced American weapon systems at a favorable exchange, why not? What has Zelenskyy done for us lately, anyway? I’ll show you some quid pro quo!
Stranger
As close as possible to rolling back what has happened since 1989. If not necessarily absorbing the Baltics into Russia or reviving the Warsaw Pact, then at least detaching as many as possible of the former Soviet satellites from NATO into a cordon sanitaire.
It seems evident that
a) the US no longer wants to defend or support Ukraine
b) the US no longer wants to honor its Article 5 commitment to assist NATO members who are under attack
As the US has become unreliable, European states need to decide among themselves how committed they are to Ukrainian security and to the doctrine of mutual defense.
If Europe cannot present enough of a united front against Putin, would he be more inclined to push further west into free Ukraine, or would he instead attack the Baltic States*? (*where I live)
Ukraine is a higher priority for Putin. And the Baltic States, unlike Ukraine, are NATO members. However, if other NATO members did not provide direct assistance, the Baltics obviously would not have the means to resist a Russian invasion the way Ukraine has.
I feel like some people missed the sarcasm tag (/s) in my post 
You may have intended the question as sarcasm but there are plenty of people are making the same statement in askance of the notion that once sated by consolidating Ukraine and deposing Zelenskyy through a window Putin will not try for more, as if he parallels to 1938 Czechoslovakia aren’t clear.
Stranger
Right now it’s in Ukraine’s interests to simply stop contesting the war, sign whatever agreement is put in front of them, and then abrogate that agreement when Russia invades the Baltics or wherever.
Peace deals with Russia are worthless and temporary. Only a fool would consider actually being bound by them.
Given that the United States is an unreliable ally at best, and at worst might aid Russia, it’s probably for the best that Europe forms a new defensive coalition for their mutual defense. I can’t help but think NATO is pretty much dead as far as the United States is concerned.
He’d gain another country.
He has a unique window of opportunity here. Nobody other than Trump would consider standing by while Russia invades a NATO ally. So Putin will want to take advantage.
Almost every country on earth is below replacement levels. Why is that a problem for Russia?
It’s only a problem for countries which care about their citizens, and let them vote.
They don’t need to invent anything new out of whole cloth, because the European members of NATO are almost exactly the same as the EU. In the EU but not NATO includes just Austria, Ireland, Malta, and Cyprus, and in NATO but not the EU is Turkey, Norway, UK, Albania, North Macedonia, and Montenegro, several of whom are already applicants to the EU. If NATO falls apart due to the US pulling out, it would be unsurprising to see the EU add a military alliance aspect to the economic.
Latvia, Lithuania and Estonia are all, IIC NATO, and their military is dinky.
Putin wants to bring back the old Russian empire- that includes those three + Ukraine, Belarus, Finland, Poland, Moldova, Armenia, Azerbaijan, Georgia, Kazakhstan, Kyrgyzstan, Uzbekistan, Turkmenistan, Tajikistan, and wait for it… Alaska.
he also wanted to take UKR swiftly … and he is still choking on it and lost a part of Russia
so there is “wanting” … and there is “canning”
True, but Ukraine had a reasonable military, not so those three dinky states. Not to mention, it is easy to get aid to Ukraine.
If Putin gets peace in Ukraine- I predict he will keep crimea- he will turn to those three- or just muscle Belarus into giving in.
lets be realistic here: the reason why UKR still stands lies (ha!) not within UKR, but in the support they got from the west (mostly advanced weapon systems to allow them to go beyond the 5 mile front line) …
the same holds true - in a more condensed form - for the baltics.
Any agreement will cripple Ukraine. Russia’s plan is to reinvade later when the time is right.