As mammikoura says, the most likely reason they're not coming back is that they're glitched in the landscape: a field dressing often solves that.
A good thing to get your squad mates into the habit of doing is telling you what their status is re are they alive or dead?
It's all fine and well when your team mate shouts "I'm down! Medic!" in finest Hollywood fashion. But they fail to convey the most important info: are they down wounded? Or are they down dead, no chance of recovery.
Getting them to do this helps you fulfil your role more efficiently. If they're only wounded, get them to tell you how many seconds they have left. This helps you prioritise who gets the zap first.
It's really about you setting the rules for your squad and making sure they abide by them: get them to relay alive or dead status and you're on the way to saving your defib charges for those that can benefit from them most which in turn means you'll spend less time trying to revive the dead.



