I remember someone saying that 100% of the ORD 747 grandfathered pilots didn't come back, and they filled vacancies outside the protected slots. I don't know if someone can verify that or not. Its likely that a lot of the IAH 787 already are planning a move to the west coast, etc so maybe it doesn't end up being a big deal.

I know a few people though, that left IAH 787 FO to go fly the 747 (just for bragging rights) and said they would come back when they shut down the fleet, but now they can't, because the BES was closed for them to displace to it, even though they flew it previously, because of the way it was closed and opened again.