If Putin fails this, it is over for him. There is no turning back from this and continuing to lead the country. The whole idea of invading can be classified as crazy and was not expected to actually happen by many. I just wouldn't underestimate him if he is backed into a corner.
Does not have to be the case. If the loyalists around him don't topple him he can sell this one way or another to the Russian public. I think a lot of people outside of Russia think it's some heavily censored, propaganda-fueled place. Most Russians are actually very skeptical of what their government says, it's very common to roll one's eyes at official statements. However, this does not change the wish to remain powerful even if just in a self-preserving image. If that does not work, the victimhood card also is often used successfully. If Putin can remain popular and the cronies around him don't replace him it would not have to be over for him at all.
Many things can be sold to the public, but it's particularly hard to sell a steady stream of coffins, and especially so if you can't showcase significant military gains.
