I do think its worth not doing the "Antimagic field + grapple" scenario again. Not because of anything wrong with it, but since the goal is for the simulation to showcase "any old party vs Vecna", it would be good to see groups winning or losing trying different methods. If one method is always working or failing, then people could point to the method as the problem, rather than Vecna.
Perhaps I would love to see the party just go in with very simple tactics, because I think they will still beat Vecna, and that's very telling. Just go in and beat em to hell!