No Room For George said,
"I can't help but think that the WT would leave itself open to lawsuits."
Yes they would, but consider this...
Who would sue if the ban on blood was lifted? Wouldn't it be relatives of someone who died because they refused blood? If the ban on blood was lifted quickly survivors of the deceased would say, 'You mean our mother/father/son/daughger didn't have to die after all? He/she followed your policy and lost his life thinking it was the truth, and now you have taken it back? We are taking action against you for loss of life!' No doubt when attorneys figured out how to win such cases the law suits would fly against Watchtower.
How to avoid such suits? Wait until all those who could possibly bring suit have passed on. But that will take decades, so what does Watchtower do in the meantime? Keep the blood policy on the books, but do not DF or DA for it.
As Refriedtruth said, the Sociey can mealy mouth it's way through this, providing plenty of loopholes, giving counsel privately that isn't in print, so that no one has to die because of not receiving blood in the coming years. Then, decades down the road when the coast is clear - meaning there is no longer a threat of suits from survivors - quietly drop the whole matter. Maybe the Society will even claim it had been a conscience matter all along and that 'some back in those days misunderstood' (that's certainly a method that Watchtower has used before).
This would be a long process, but it seems the Society's blood policy is in a state of transition now, and has been since major changes took place in 2000.
These are only my thoughts, but a scenario like this would provide a way out from under the organization's horrible blood policy eventually, and avoid most of the law suits.