You won't see their replies obviously (split thread) but if you delete the message, it gets deleted from your followers, but won't continue on to the server that your server blocks. So a copy will continue to exist.
I just treat the fediverse as a big chatroom/reddit thread that can never be deleted.
Treat the whole internet that way. You can't forcefully delete things from other peoples computers/minds. The best you can do is request.
I deal with this by posting almost nothing under my real name and switching usernames regularly.
I don't think that's necessarily true.
While I don't know if the IRC Server software supports it, there's no reason you couldn't encode some kind of unique tag into the stream of IRC messages sent to each client. Unless you were running two clients and diffing their logs you wouldn't notice.
It could be as simple as seeing additional events, or modified whois/client information on join/leave, or even completely fake client join/leaves.
If you control the IRC server, there's nothing stopping you from modifying the events sent to every client in a way that lets you identify that client.
You bring up an interesting point about GPDR and aggregate logging. The same probably applies to mailing list archives.
I never came across a logger, though, when I was still active on IRC. Are loggers a more recent (as in this millenium) development?
Every fairly modern chat solution, Skype, Discord, Slack, etc. allows you to see messages while you were offline. Compared to things from the older eras of messaging like AIM and YIM, when generally you couldn't even message someone unless they were online as well.
So it's not surprising to me for IRC loggers to be a relatively more modern element: They're filling in a gap IRC has with modern chat clients.
There aren't many uncovered edge cases I can see.