I honestly can't see how he can concede, it's all or nothing. He probably feels (rightly) if he pulls back now it would weaken him irreparably and it would only be a matter of time before one of generals decides to take matters into his own hands and kill him.
I suspect he realised that after a few days, and especially as the heavier sanctions were placed. He doesn't want this to be seen as a waste of time to the Russian public.