Another option would be the removal of merit which will go back to the sender. But it's much harder to implement I guess. I agree that merit abuse went too far on this forum.
For example, I have merited one of Welshs reply and then a minute later the topic itself got deleted. You mean the merit I sent to Welsh will be debited and credited back to me? IMHO, that is kind of blurry suggestion. The reply is of quality. It will affect those posts with quality, but, at the wrong topic or affected by new forum implementation rules which only discussed on staff board.
The rule should not affect the merited posts if the entire thread gets deleted, but if an individual post is deleted, either by a moderator or by the user himself, then the merits should get burned as @hilariousandco has said, because in that way, the one who sent the merits with the intention to abuse the system would get nothing back, neither the receiver would get any benefits out of that.