....but they wouldn't have to surrender. They could just declare a ceasefire and keep the lines as they currently are. Realistically, what other choice do they have? They can't get those territories back on their own, and they're locked in a war of attrition they can't win.
The Russians would likely be careful about any more expansionist designs. I don't agree that they would see how this tactic of expansion works. We have to play it more like a game of chess and consider the entire global situation, as there are other countries in play here. Iran, North Korea, China. There are multiple countries which don't share the Western perceptions of geopolitics, and we have to consider their point of view and how it appears in their eyes.
There are definitely risks which could lead to WW3. My view is that, for the moment, just stop fighting. They don't have to surrender or yield anything, but just an agreement to stop shooting at each other. Perhaps they can at least do that for starters, and then slowly try to work towards some sort of peaceful resolution.
What are the other solutions? We could keep sending them military aid and equipment, but their manpower is not inexhaustible. The Russians have a larger pool to conscript from. They grow enough food to feed themselves and they have the resources and infrastructure to go in for the long haul. In 5-10 years, we'll be in the exact same situation, yet more lives will have been lost. What is the purpose in that? At best, it's a stalemate.
Having said that, I acknowledge that we can't tell the Russians or Ukrainians what to do. If they want to keep fighting, then it's really their choice in the end. All we can really do is ask what our government can do about this situation. Is the government even telling us the truth about it? That's a perfectly valid question, I think. You and I both know the government's track record on certain things.