The least worst outcome now would be the concession of the Donbas region as notional "independent republics" - probably including the entire littoral to the SW enabling a contiguous land route to Crimea - and withdrawal of the Nato application pro tem. The alternative will be total destruction of Ukraine and, quite likely, the introduction of tactical nukes - and probably a nuclear ("nucular" in American speak) WW3.
Following that appalling necessity, a united world, minus China of course, could proceed with the progressive destruction of the Russian economy which would almost certainly cause Putin to fall by one mechanism or another.
Having just watched the Eurocrats congratulating one another on their moral stature I fail to see how the conflict can be successfully pursued without catastrophic escalation, no matter how many condemnations are issued. As for "no-fly zones", far simpler to declare war on Russia directly since that would be the inevitable outcome.