No, they won't be defeated. They won't have time. But another question arises: will a spell be available?
As Alex_R put it, tactical problems will then affect not only Sylvan, but all factions except Haven and Necropolis... And that turns out to be complete nonsense!
However, Sylvan has excellent luck (and morale is also good). And that's also a nice bonus in battle!
Auto-translated
