Hi, ATW, Aaron,
I know of several people with GG and DR with Bvlgari at this time; service is proceeding as normal (they even kept Meyrin open just for service, though that too will be consolidated to Le Sentier.)
No one can predict the future; does Automobili Lamborghini guarantee to service all Lambos every produced? (no, though they try to be helpful, they also acknowledge that pre-Audi Lambos are not as deeply supported as post Audi Lambos.)
Does Rolex, with NO change of ownership, service their chronographs from the 1960's? No, I know from personal experience.
So this has nothing to do with Bvlgari's business decision in moving DR and GG under the Bvlgari umbrella, and as a business, I doubt they will "leave their customers hanging" in the near term.
Different issues apply in the long term.
TM