I'd definitely be curious to know what went on. The loss of 3 years of posts is not a good sign... Seems like a "where was our last good backup, uhoh..." situation...

As to the DB with the death chats, no idea on the size but I know that mysql can certainly handle quite the size.

I'm more suspecting a lower level issue resulting in some type of corruption that in turn necessitated the restoration of an ancient backup.