if you delete your post, sender should be refunded. it means that you didn't want the merits, they could be used for others actually wanting those merits.
Great. And how exactly would this work, considering the one receiving the merit would also get sMerit? Or will you let them keep the sMerit? That would lead to a lot of merit farming.
Will you cut off the chain of merit being sent out? Then that wouldn't be fair to the ones who actually have good posts and were sent merit from the chain extending from the deleted post.
Yup, the merits should be refunded and the smerits should be cancelled. It would be like a transaction which is void ab initio. The chain of merits can still be considered valid, if the senders had enough smerit (excluding the ones in this transaction). Otherwise, it can be cut off.
It is fair - good posts were considered meritorious by people who didnt have enough smerits. Therefore these posts were not merited.