As long as Ukraine is supplied, they will be able to stop Putin. They've proven that over the past 3 years. They are not ready to give up, and that is their call.

You can't think of this as a conventional war with big tank battles and dogfights. Ukraine has no navy, but has managed to cripple (and neutralize) the Black Sea fleet. They are outnumbered in armor and artillery, and yet are inflicting more casualties and equipment losses than their Russian opponents. The Russian air force has to stand-off at great distances, or be shot down. Which limits the ordinance they can use. Their helicopters don't have that range, and if they get close enough to be useful, they are destroyed. So they have mostly been neutralized.

What should have taken a week by conventional thinking has dragged into three years, and the Russians still have not achieved their objective.

If Russia had deep assets (personnel and materiel), Ukraine would be doomed. As it is, they are going to be out of armor within about 12 months, and artillery within about 18 months (or maybe it is reversed...I forget, and am too lazy to pull the charts up again). If they are supplied, Ukraine can easily hold out that long. If they want to. Which, evidently, they do.

Anyone who says otherwise is not really well-informed, and is thinking big battles with lots of drives and breakouts. That's not this war. Not even close, really.