I won't say that all is lost. On a global scale, we have our army and our will to resist. That truly counts for a lot.
Europe has mobilized after Vance's speech. And if American troops withdraw, I believe even more will mobilize.
In the minds of the current EU leaders, Ukraine is part of the EU. And that is very good news. (As it could have been with NATO).
If the Americans leave Europe, then essentially the only non-Russian army on the continent will be the Ukrainian one.
The Trump administration is not "abandoning" Ukraine, but acting in its own interests and preparing for a confrontation with China. Our problem here is that we are completely dependent on the USA and their political will.
Our task is to maintain the army, join the EU, create defensive alliances, and be ready for war.
The next 10-15 years will be challenging.