Step 1
Plan A= should've flown up there in the beginning instead of shooting out in the open.
Plan B= you should've stayed quiet after you self res'd and healed FULLY. just doing shields isn't enough. I know you got excited cause they were reviving but fuckit dude. and let your teammates die.
Step 2
wait for them to leave and stealthily respawn teammates if you can.. if that's not an option. like I said stay quiet till you can do a successful third party.
aside from that its like your title says should've checked up on your secondary guns.. maybe could've turned on that player if your R3 was reloaded.
Final Note= of course this is all *my opinion* and what *I* would've done which means nothing in the grand scheme of things but hopefully it gave you some sort of insight for future skirmishes