We urgently need to fix the issue of ghost instances/communities which defederated/got deleted.

The longer I use Lemmy the more I run into posting on places where my posts will never reach anyone apart from my own instance. And then there's a growing amount of communities which display normally for me but if I actually open them it shows they were deleted. We desperately need a way to make them send information to all instances which used their information to remove it as it got deleted. Or a signal from an instance to other instances and their communities essentially asking them if they're still federated/existing. Of course not frequent, that'd waste resources. But happening enough not to make people lose time screaming into the abyss. Not to mention the utter waste of server space keeping content which cannot be used... :(