FB is a natural home for him. (Not a compliment, by the way.)
With some things like the failed alternate vote referendum I have read people blame Labour more than the Lib Dems. However, he clearly lacks charisma and skills in hindsight.
I don't think anyone at Facebook will force Nick Clegg to do or say anything but I'll be shocked if he has any serious decision-making power within Facebook. I'm trying to avoid saying he is a rubber stamp but it is difficult to say he is much more when even ex CSO Alex Stamos clearly had restrictions (if you read between the lines).
Given the successful spoiler/enabler role of the LibDems in UK politics, there's a good chance he doesn't think of his record as one of failure on any level.
Interesting, he has already deleted all of his tweets, including the anti-Brexit ones - not quite the action of the absolutely committed anti-Brexit campaigner he claimed to be.
(To say "FB wouldn't let him keep them" misses the point. Someone who was genuinely committed to stopping Brexit would never accept a job which might conflict with keeping them.)
In that case, he has a long and productive career ahead at Facebook or perhaps at a company like British Petroleum.