Those are automatically exercised at expiration.

If the holder can afford to exercise, and I can assure you that most RH users cannot afford to exercise a single contract(at least on most commonly traded stocks).

Otherwise it's on the broker to sell it at close to someone who can afford to exercise. And who knows if RH pulled that off or not.

I haven't seen official statement, but I did see a couple reddit threads where Robinhood exercised ITM calls without enough funding in the account, then collected the shares and paid the cash difference.

https://www.reddit.com/r/wallstreetbets/comments/fcqkmo/so_r...

There's also some threads where it looks like it did not go so well...

https://www.reddit.com/r/wallstreetbets/comments/fd2eko/upda...

If their systems are down, were they actually exercised or is that managed by another brokerage?

That's an interesting question. I suppose it's hypothetical in the sense that they now have to look at "what if" those options had been exercised; but unlike a spot trade that someone "would have" done, Robinhood might already have had obligations on its end of the original options trade.

Absolutely. Why wouldn't they be?