That's the mod's problem. Why are they removing topics that are flagged ? Any solution ?
See this one for example:
I think it was deleted because the topic is "insubstantial". The solution is not to rely on other people's topics when you create a Flag. Don't link to for instance the scammer's own topic.
Those types of flags should be removed, I hope theymos is taking a look at this otherwise anybody can create a flag then delete the thread associated with it.
So far, only 5 Flags have been removed. I don't think theymos wants to spend too much time on it, it's up to the community to Oppose invalid Flags.
Also if anybody is banned should their flags be automatically deleted too? What are your views?
No. They can still be valid, just like feedback doesn't get wiped when someone is banned.
Is it possible to delete a thread created by yourself ? I was thinking only mods have that option.
Users can only move their thread to Archival. Mods can move it to "the trashcan". But a user can just create a worthless thread, use it as Reference, and then wait for a Mod to clean up his thread.
Or a user could simply be Nuked, that removes all topics opened by said user.
Surely if a flag exists for a thread that no longer exists it means the alleged evidence the flag was created on is not available therefore the flag should not exist either.
I wonder what the community consensus is on this.
I don't think this community will ever reach consensus on anything

My opinion: if an Active Flag doesn't have a valid Reference topic anymore, someone should create one, create a new Flag, and the current Flag supporters should stop supporting the old Flag and start supporting the new Flag.
I think that's the proper way to use the Flag system, but it's a lot of work.