I am not an expert either, but I would say that you have to rehash it either way if it grows (or shrinks). Tombstones as I understand it, are a way to "mark" deleted entries off of the hash table. Having these deleted entries marked ensures that your hash table doesn't break its "search chain". This is important so that you still can find entries that are put at another index when one index ("bucket") is already occupied.

However, I also don't shrink my table, once it grows. It stays grown. (Another drawback of my lib I suppose).

Thank you for the feedback, I really appreciate it! :)