There was a similar post on this, but it only covered users who had answered the question, but not users who flagged it or commented on it.
I find it quite aggravating when I comment on a post, and then I come back to look at it again, and I have no Idea where it went. I try searching for it on a site it might have been migrated to, but I still am unable to find it.
I think it would be nice to either notify all users involved in a post when and to where it is migrated, or, (even better) in the user page, keep the link to the answer (or comment if you're looking in "activity") there, and just have it forward wherever the question has been migrated to. (or both)
In addition (This may require a separate question, but I'm not sure. Let me know about this one) It would also be nice to be notified whenever a flag is found helpful.
Edit: As per the comments below, I realize that it would be best to be opt-in (per-question), so that users who don't want it, don't have to be notified.