Do you think the dragon has figured out the sword's properties? Maybe he's planning to use it against the party to dispel their beneficial magic. I'm pretty sure that only works when Roy wields it, but maybe I'm wrong, and dragon might not be aware of that if it is the case. I probably wouldn't want to waste slots on dispel magic / counterspell instead of control or disabling if I was him, and the sword can deal damage in the same action.