I would have to refer you back to
Beau. Putin has played his cards, this is about power and returning Russia to its former glory of a superpower. Anything short of that in the eyes of a 70 year old man will not do. He is what they call a dead ender, there is no negotiations with that. The only way you change that is by force, Russia economy and military needs to be decimated, it's either that or the Russia people rise up in a coup. That doesn't seem likly right now as it is early days still but as the economic sanctions bite and people are starving in the streets that may change.
There is another way. One of Putins' Generals could assist his suicide, like so many of Putins' opponents, with two rounds to the back of the head.