Anything less would be an admission of failure, and Putin cannot afford that now.
I believe the Russians have two options:
Either, stand off and bombard Kyiv with missiles and air strikes (chemical? biological?), possibly for months, hoping that resistance will eventually crack and the defenders will give in.
Or, what they may be trying to do now: surround the city and impose a close blockade to starve it out. This would require a well-manned perimeter of at least 100 km. The opinions I have seen suggest that the Russians lack both the forces and the coordination to do this effectively.
Either way, Putin’s pretence of ‘liberating’ Ukraine from ‘Nazis’ will be well and truly finished.
Russia blames Kyiv for 'catastrophic' humanitarian situation in Ukraine.
A senior Russian defence ministry official said that the humanitarian situation in Ukraine continued to decline rapidly and blamed the actions of Ukrainian fighters,
the Russian news agency RIA reported.