Nothing, that's not the point. The point is that the developers stop work on it and eventually it stops working. Then the Switch 2 comes out and Switch 2 games cannot be emulated. Nobody thinks that Yuzu, in the current state, will stop being available.
They can. But I guess there is a limited amount of potential Switch emulator developers, and people who have an interest in that are already working on Yuzu. A new team can absolutely happen, and will also get sued until no one even tries anymore. I guess that's the idea on Nintendo's side.