Believing what the deep-state Kremlin apparatchiks say... is a waste of time.
This is the sort of thing that makes it very hard to see an end to it.
A Russian withdrawl results in an overwhelming NATO presence in Ukraine, and the eastern border of Donbas is less than 100 miles from 4 million barrel/day flow through Volgograd. There is no way in hell any Russian leader can allow that sort of threat. That would be inconceivable.
In contrast, a military coup in Kiev must kill the CIA and MI6 people surrounding Zelensky before they can get to him. This is much of why he spends so much time outside the country.
So . . . maybe assassination outside the country is the only way.