Do away team member ever return?

[Nobody]

Randomly got Ranger, did one job with him and asked to do a character mission, after doing it he has been gone.
Bought Vamp, randomly said that she needed a break or something, now she's permanently away.
No matter how many ingame days pass members that are away never return and are just sitting there cluttering the menu.

[[BR] Titanoner]

They do, sometimes they just take a LONG time. I had the same question when Runaway did the "break" thing and she was gone for iirc, like almost the entire campaign (Which is roughly two weeks, max). There's no solid answer. They just randomly come back. Had another do it for like, 3 days.

[Cryptic]

Takes time. Just go without them for a few in game days

[Taberone]

I think Ranger's story missions are tied to Dollar Dragon? Once I eliminated Dollar Dragon on my last run, I stopped getting the Vietnam Flashback missions for Ranger and he was set to "away" for the rest of the run. I think you might have to delay defeating Dollar Dragon until Ranger's story is over, but I'm not sure.

[Your Neighbour]

Not sure if it's model recycling or lore, but the captain does look a lot like Dollar Dragon.

Also he comes back in future games. When you do the final Red Star he will retire for that game until you do another playthrough.