IMO...
From overall C&C for a side...down to each squad member...the SOPs should be well known (and understood, and accepted) well before. If guys are well on the ball all that's needed is a quick briefing at the game...if they're random individuals it might be a lot harder. Best thing to do is to split up the random individuals and tag them along into a squad of guys who have things worked out already.
Since each person on a squad knows the SOPs...then when they take a loss there's a way to check in with everyone, a way to quickly assess how you're doing (ammo, strength, etc...) and a decision point if you can continue or have to GTFO and regroup.
If a number of small squads are working together (or even in the same area) they might join together until things get sorted out.
So far as having guys link back up it's always a good SOP to never have a single guy go anywhere. Dead guys can head back to respawn together...live guys can head out together to regroup. A little bit of C&C can go a long way....linking guys back up with their squads, tagging them into other squads for a bit until they can hook back up, etc..
Everyone having a radio is a good thing...95% of the guys should be doing nothing but listening anyways.
Not having a plan/SOP...letting guys go off on their own...not having a way to communicate....that's the perfect combo to have guys go off and never hook back up with their squad.
That said...that all works in "milsims" and not really in an all day skirmish with a bunch of random individuals. If you've got random individuals...or even little groups of guys who don't know what's what...then tag them with other groups who do. It'll probably be a much better day for everyone.
**********edit after your last post*******
Say you've got a squad of 5-6 guys....
- if one is hit...they should just hang out and see if anyone else from their squad gets killed...or if anyone else from another squad gets killed....before they head back to respawn. Wait around (be dead though...not in the way of the fight)...don't go back alone.
- if two or more are dead...they should wait around until the fight is over. Their squad may take more losses and decide to regroup...in which case they can all head back together. Otherwise...the dead can head back together.
- if you have to head back alone...it's not a bad idea to either set the RV point to be...the place where you died (the other guys can lay low and wait)....a designated spot (maybe where your squad has stashed their packs/extra gear/etc...)...or an RV that your squad sets as you move along. Might be a designated feature...i.e. the bridge...the makeshift fort....the "big pine" (old FTF landmark). Whatever you set it to....both the squad and the respawning guys have to know to meet there...and how to get there.
Being able to communicate is obviously important.
If all that seems like a lot of waiting around...then encourage people not to rush in a get shot.
If guys aren't trying to link back up with their squad...then they're really not working together are they?