If the post is already merited and needs to be deleted, mods could also delete the accounts involved.
Wow. I think we need to hold our horses a bit. We may find Merit abuse that is being camuflaged by deleting the post, but accounts are not deleted unless it clearly leads to account farming uncovering.
lol, ok...
anyway, the impossibility to delete a merited post would be a good idea and would solve this problem...