So I think the answer is, it varies. Like people are using the GDPR to argue that Reddit must delete their posts and not retain their content, and I think that's the correct answer.

I am planning on doing this but only for my own Reddit posts and comments. I'll recreate my side of the convo in the fediverse and delete it from Reddit so any useful advice or interesting tidbits from me, people will have to come here to discover.

That said, there is a lot of useful content from Redditors who are no longer around (some from well known people who have since passed on, for example). It's a shame we can't move that content over here but privacy and copyright laws can get very complicated. Better to do things the right way.