Wouldn't it be better if they made it possible to find replacements for lower level keys? For an example, if you need to do 10+ to get the best out of the weekly chest, then make it so that finding replacement for leavers is possible if you're doing a 10+ or lower key.
Also, to prevent people from abusing this system, make replacements only possible if one of the players has left, not removed from group (to prevent toxicity)