They will still need to rest in the future. es3tag is signed as a master of all trades, so if device needs a break, I can assure you that es3tag will pick up the awp and xyp will go back to his role (if he is back.)
He also had a short stint as IGL in heroic. He truly does it all.
I think everyone, including himself, is surprised at how well es3tag plays in the astralis jersey. Nothing bad about that for anyone, when you take the overall plan into consideration (noone is getting benched, players are playing on rotation.)
IMO xyp9x is miles ahead of dupreeh in many aspect of the game, but positionwise it's a clash which is easier solved by subbing duppe with bubzkji.