The newly annexed land will defended and remain part of Russia.
The Russians will dismantle or take more territory is guarantee the security of Russian territory.
There isn't anything that will change that.
Just because Russia claims territory is no justification for keeping it. There is a strong difference of opinion being expressed on the part of many other people.
It will, of course, come down to force and resources. As of now it does not seem that Russia has these. Especially given its poor social system and leadership. Indeed, the larcenous spirit in which the Russian leadership undertook this adventure is itself an aspect of its deficiencies. Corruption is the seed of incompetence.