The ruble is tanking hard. This is a timed thing, I think. Two things are critical to fight wars:
-Soldiers getting paid and having resources to ease frustrations of fighting.
-Citizens not feeling too overburened with side effects of the war.
With the ruble tanking, I think it is only a matter of time before an overwhelming amount of citizens are protesting and the soldiers start to turn on the government or throw down the weapons and flee.
I would not be surprised if Putin is taken out by a former ally's assassin in order for the oligarchy to survive by making him the scape goat and acting like they are the good guys.