If you are talking about players who are getting stuck in Expo they're most likely level 100ish or below.
A level 160 maxed-rune angel dragon will not die against their heroes (and her basic attack might even kill them). Maybe spectral Drake could charge in time but then again we are talking about players who are relatively inexperienced and don't have many heroes or know much strategy. They're just going to get stuck sometimes. All players have gone through it.
Next thing you guys will be asking me to take runes off my heroes lol. Probably still wouldn't help. Instead of posting here, just tell your low-level Guild mates that the problem will stop as they get stronger (and help them learn to how to do Expo better, to better manage their resources, and to prioritize important Heroes).
I have a VIP zero, lvl 95 account (with no legendary skills until a couple days ago and no dusa) that I almost never play and I can still usually get through insane expo if I really I try.
With all the double experience and crafting bonus days and gear tickets and countless bonuses over the past 6 months, if players are still that low they must really not be playing much at all. Losing them from the server is likely not going to hurt anyone. If it looks like the player has a lot of promise and enjoys the game but this issue is for some reason a deal-breaker then just help them through it. In my experience if people really like this game they're going to level and play it regardless of the Expo problem. If they are so frustrated that they leave because of this issue, they're probably going to leave for some other reason or frustration in the future anyway.