I wouldn't bet on any 2021 European race going off on schedule. Unless the vaccines currently in development show remarkable efficacy without significant side effects very soon it's likely the organizers will plan on bumping every race a few months later to be better ready.
I'm still surprised by how smoothly the Giro, TdF and Vuelta went off in 2020, considering the last minute prep. With that kind of experience under their belts, perhaps the organizers will delay any decisions until a few weeks before the usual starts for those races and hope for sticking with the traditional schedules.
It may be harder on the cyclists than on the organizers. But that's part of what made 2020 so exciting.