To get events, just scrape the Facebook website using Selenium and Python. There are online tutorials for this. Harder than it should be, I'll be the first to admit, but easier than blockchain-based systems. (Blockchain isn't the appropriate solution for social media; use a proper federated protocol like ActivityPub or XMPP.)
Then you can just reply to Facebook messages on something other than Facebook. That'll annoy your friends a bit, but that's the cost of them still using Facebook.
The problem with Facebook is not that it's hard to get your data off. It's not, really. The problem is that you have to be a programmer to do so; and blockchain stuff doesn't fix that problem.
As you can imagine it's kind of hard to push back against these bad actors by threatening them to do the same thing to them, due to their sheer size.