The only thing I can see is if these 300,000 reservists he's planning to call up either don't go or refuse to go, even he can't afford to upset his army, so my hope is that the Russian people see sense and refuse to fight.
It looks as though these lads are either being arrested, for refusing to go, or are heading for the hills while they can, it seems that the truth has been slowly seeping into Russia over Ukraine.
Putin is struggling, his {mainly} conscripts, that were first sent, didn't want to fight in the first place so their need to be triumphant is not as ingrained in them as it is a Ukrainian fighter.
Putin's firepower, although vast, is no match for the up to date sophisticated equipment being supplied to Ukraine by the West, you only have to look at the ground that Ukraine has retaken in such a small space of time to realise that Putin is being totally "outgunned". His threat of using nuclear missiles is {hopefully} just that, even he must know that launching these missiles will do massive damage and cause an horrendous loss of life, so he must weigh that up against most Western countries would retaliate and there won't be much left of Russia after that.