Yeah sounds like a bug, notifications are supposed to be wiped for a deleted post. Will look into it.

That's part of it, yes. But the main issue here is that if the thread has been deleted, I'd like to get a notification something along the lines of "X has deleted the topic titled Y" instead of wondering where the thing disappeared?

I'll think on that point.

Any time a user or mod manually deletes a forum post, it will now notify people who followed it.

I'm not doing it for when a user deletes their account though, as that will end up quite expensive on SQL resources and could potentially be quite spammy to users on notifications if they did a fair few and people followed a fair few. But at least this way if it was a manual deletion, users know.