What happened to you is the exact reason why I keep all Linkedin contacts on my local excel spreadsheet. Sure, if Linkedin decides to get rid of me will feel bad at first, but I won't feel powerless.
I have always been agnostic of closed platforms. But for whatever reason, LinkedIn never came to my mind as a platform to also hedge against. LinkedIn just never crossed my mind in that respect. But right now, it has happened, and its too late.