I really want his coat. My last save before this quest is from three hours ago. I don't want to have to reload so I'm just wondering if there's still a way for me to trigger it. Thanks!
Sometimes he's hiding on the blimp instead of at the base. You can no longer get his coat after you destroy the ship, sorry. You can only add it with console commands, maybe wait until they release mod support for console people.
The only way to have no chance of getting his coat is to do the Minutemen mission for destroying the Brotherhood. Of course, you can get the coat by boarding the Prywden and killing Maxson, then escaping before doing that mission. The Institute mission allows you to grab the final Brotherhood of Steel Power Armor that is only reserved for Maxson. Of course, you have to be quick enough to loot his body before you are teleported away from the Airport. The Power Armor just has a paint job that changes the insignia on the left gauntlet.
He should still be in the ship somewhere unless you somehow killed him before that mission, if not, he should still be somewhere on that ship. I saw him at the Command deck or sometimes, outside on the balcony. He likes to stare at the balcony when not in his room. I'm sure you can still get it, just keep looking for him, he may be covered under other dead bodies.