Years of habit and indoctrination is a powerful thing. It would take a while for JWs to switch gears and there would still be oldtimers and fanatics that still would shun.
Yup.
There are still millions of JWs who refuse any sort of blood fraction, even though the ban on them has been lifted.
Heck, I've even heard old-timers (and adult children of old-timers!) who refuse to cook in aluminum cookware.