As the title states if you play against a cheater but they are not banned during the game you played against them but instead end up getting banned down the line in a later game you should be reimbursed the mmr you lost.

Other games like R6 Siege do this and I think valorant should do the same. Having played against a blatant cheater today (a guy who put his twitch stream in the chat which we then opened and saw him hacking on stream with walls) it is very frustrating.