All they have to do imo is this:
1. Stop taking any action against individuals who accept blood products.
2. Issue a statement that the technology has become so advanced they simply cannot keep up with it. They can continue to say that the Bible tells us to "abstain from blood" and it is incumbent upon the individual to discuss the matter with his doctor and act in good conscience.
3. If they are asked why they no longer DF or DA (perhaps in a Questions From Readers), they repeat item number two above and could also add that the WTS cannot afford to be drawn into legal responsibility for the actions of individual JWs and/or their doctors.
I could probably refine these arguments further, but that is essentially how I believe it would be done. It would take a number of years for the average JW to understand what really happened. Perhaps the majority would miss it completely. They simply quit writing and giving talks about it, the same way they quit all of the silliness on vaccinations.
Would there be some lawsuits? Probably some would try, but I don't think it would be anything like the nightmare they are dealing with on child abuse.
The upside for the WTS? They lose one of the primary criticisms that causes them to be labeled as a dangerous cult. The eliminate future liability. They make it easier to attract converts. They free up all of the resources currently committed to HLC and HIS.
If and when they are sued, they can either say that their policy really hasn't changed. They still teach JW's to abstain from blood. I think it would work and ultimately be a plus for the WTS.