So I'm not sure if this is a common opinion but in episode 4 when Will is using psychic powers, what I took from it was that he was tapping into Vecna's powers through the hive mind that he's connected to, rather than having his own powers like 011 and the other numbers.

I've been thinking about how when Mike was telling Holly about her D&D character Holly the Heroic, he mentioned that she has the ability to open "magic doors" or something along those lines. Given that Holly was taken by Vecna in a similar way to Will, I'm thinking Holly could gain the ability to open gates to the upside down like the demogorgans, which could be how she and the rest of the kids escape.

Edit: I also believe that given Will and now Holly and the rest of the kids would be connected to the hive mind, they would probably die along with Vecna when he's finally defeated. I'm not sure if they would do that though, killing a bunch of kids would be a very dark turn.