Ideally, Vader survives to late game -- he's pretty strong there (as well as early- and mid-game), but may prove delicate if subjected to focused fire. And enemies are incentivized to murder him fast, knowing the problem he'll be. He's quite the hammer if he's getting locks, and if your team can wield enough firepower on foes you can turn the odds in your favor quite quickly (especially if those crits land really hard).
Basically, if it's down to vader vs one other ship, Vader has a fairly sizeable advantage thanks to his repositioning, initiative, crits, force, etc. So it can be a good idea to either keep him alive with clever & cautious flying, or draw attention away from him with equally threatening allies.
Interestingly Emperor Palpatine doesn't help Vader as much in this edition unless vader's spending his force like crazy. There are supports that help him, but his generally allies need it more.
IMO, a TIE Defender works quite well here. They're monster ships with good firepower and maneuverability, and they draw attention from vader well. And if the enemy kills vader first, the defender is a good late-game threat too. Then add one or maybe two tie fighters to act as blockers, cleanup, and fodder (e.g. Seyn+Marksmanship is scary in her own right, since it's impossible to avoid damage if she lands you in bullseye).
Alternatively, a TIE Punisher (often Redline) or a couple TIE Bombers/alpha-class star wings with Proton Torpedoes could provide a shock of damage for early-game knockouts, probably also drawing enemy fire away from vader as the foes try to kill or outmaneuver the alpha-strikers.
"Whisper" and RAC also make fine allies. Whisper is along similar ideas as the TIE Defender in terms of spreading targeting priority, but as more of a skirmisher & flanker than face-to-face jouster. RAC is a brick wall that absorbs hits like a champ, and dishes out good damage (especially when supported by Minister Tua).
I hope that helps!