Tico and David are definitely staying with Jon out of loyalty and because they probably still enjoy going out there and entertaining the fans. They are both well aware of the current condition of Jon's voice and they probably don't care.

They've been by Jon's side for close to 40 years and they've basically witnessed the evolution and aging of Jon's voice they've likely accepted the condition of Jon's voice and moved passed it. They will remain by Jon's side until the very last show and tour.