For starters, keep in mind that this event is mainly RNG dependent. I was getting slaughtered with barely a turn. All of a sudden I beat it with barely a scratch. Makes no sense. But here is how I did it. I stacked all my best mods and made sure I had all Omegas. My only zeta was Bossk's lead. So it IS possible. I hope this helps someone!
Bossk: zeta lead, G12 with first half of G12 pieces; defense /health mods; 41k health, 47k protection, 234 speed, 32 potency, 44 tenacity.
Boba: G12 with first half of G12 pieces; speed/health mods; 27k health, 28k protection, 237 speed, 51 potency, 73 tenacity.
IG-88: G11 with only one piece short of G12; health mods; 21k health, 16k protection, 191 speed, 18 potency, 28 tenacity.
Dengar: G10 basic; speed/health mods; 25k health, 30k protection, 186 speed, 34 potency, 31 tenacity.
Greedo: G10 basic; CD/CC mods; 15k health, 18k protection, 213 speed, 30 potency, 27 tenacity.
For starters, if Dengar doesn't Stealth immediately, I put it on auto. There is no chance of surviving when R2 controls who you attack. Do NOT attack Han until it is down to just him and R2. His counters will shred squads like mine that are under geared. Defeat Chewbacca first! Use Dengar's "Blast and Smash" on Chewbacca every time Chewbacca has more than 50% TM and hope for a stun. Also focused Greedo's "Threaten" on Chewbacca and no one else (keep that son of a gun on lock down mode). When I landed each of those on Chewbacca, I used Boba's "Execute" to clear all buffs and do some serious damage to Chewbacca. At this point he was the weakest enemy, so I used Bossk's "Hunting Party" on him and dropped him down to about 30% health AND fulfilled the contract all at once. Then Greedo finally attacked more than once (which..after about 15 attempts he never did) and defeated Chewbacca. No one in my squad died. I was lucky with rng bc the AI didn't focus their attacks on any one toon. And I was IG-88s AOE attack to heal my entire squad thanks to Bossk's zeta lead. Next I killed ROLO. Her AOE is the biggest threat being high damage and sticking an ability block. Downed her with just a couple attacks. Then Lando for similar reasons: very effective AOE and he's also squishy. Down to R2 and Han. I came back to what I had to do to beat Chewbacca: Blast & Smash and Threaten. Had to avoid those counters. Then R2 is the last man standing. Piece of cake. I was lucky it only took me about 15 attempts (today..I limit myself to 25 attempts per day to avoid hating this game). I did this without a zeta on Greedo's "Threaten," But it may be a wise investment for a guaranteed stun on Chewbacca (if it's automatic on a legendary? Idk..someone confirm or deny this for readers please). I only used Bossk's taunt when my team was in danger of losing someone. I did NOT use any thermal detonators until Chewbacca was down. All they seemed to do was help the AI probably because of "Guard," again someone please confirm or deny this..I am no expert on what Guard does and won't be on to look for a few hours. Good luck gamers, and may the Force and the RNG gods be strongly with you!