Can a Skaven Warlord with Felblade use verminous valour to escape to the back of his unit AFTER he has fought?

The rules states that he "may voluntarily 'retire' to the rear of the unit at any time" unless he's being challenged.

Assuming that he has higher initiative than his opponent can't he strike then retire to the back where he can't be hit?

Pic is my Grey seer and Skaven Chieftain that I'm in the process of finishing.