Putin certainly can't U-turn, but at this point his options are really limited. The longer this war goes on without a clear Russian victory, the more it becomes an existential crisis for Putin himself.
Russian history has not been kind to leaders who botch wars. He won't need to worry about external threats, between the public and the deep state - if Russia decides he is not a chosen one, to be pickled and preserved forever like holy Lenin, then he will be cancelled. Sometimes they do it politically like Yeltsin. Sometimes it's so dramatic the whole country falls apart like with Gorbachev. Other times they just quietly take you and your family into a basement like Nicholas II, and cancel you with some bullets.
