Well if they can't beat him with raw power, they should use tactics. Long range attacks, splits in the peloton, etc.
Long range attacks vs the guy who reinvented the longe range attack. What has ever been Mas' longest range attack? 50 meters?
After the TT Evenepoel will likely be 2m30s ahead of Roglic and 3 minutes ahead of Mas and 4-5 minutes ahead of everyone outside the top 3. As soon as we hit those timegaps in GC the best they can hope for is that either he fades or bonks, or that they have a very good day on Sierra Nevada and put everything they've got into an attack on that day. It's quite possible that once they trail 3 minutes in GC, that they will start looking at each other, rather than attack Evenepoel. Why would Mas go in an all out attack, jeopardise his podium spot with a rather small chance of success? Or are they going to team up and attack him in succession as if they were teammates? Never saw that happen in all those years i was hoping that rivals had the courage to attack Indurain, Armstrong, Froome... like that together. Instead, they usually started riding after each other to preserve their spot in GC, effectively doing the GC leader a favor because now he didn't have to do it, only making things ''worse''.
With those timegaps he and his team can start riding defensively and start conserving some power. He can now follow wheels and it's up to his rivals to attack. The other teams who have a second GC option close in GC are already trailing 4.5 to 6 minutes, and will be closer to 6-8 minutes after the TT. So let's say Almeida, Valverde, Hart or Sivakov go on the attack, they are too far behind to really bother Evenepoel instantly, and guys like Yates or Hindley will sooner start chasing those guys in order to preserve their spot in the top 10, than Evenepoel has to worry about them.
So even if they manage to sneak Almeida, Sivakov, Valverde in a huge break in the beginning of a stage, Bora and BEX would help out in the chase and there is a sizable margin before they become an actual threat. They (those riders in the attack) would also need to recover very well from the endeavour and raise their level considerably from now on, since they have been dropped every MTF so far.
I think they will hope he bonks, or hope to make up lots of time on Sierra Nevada. The way he's been riding so far, they only risk getting suckerpunched the moment they try to attack him on similar terrain and be worse off.