I convince him to stay after that mission most of us know. But I can't find him anymore after I blew up the BOS predwyn and became enemies with them. Is he gone forever?

He is where you last found him or should be. Tried to talk to him and he is completely unresponsive.

Damn I didn't get his perk. It's one of the best.

As I understand he basically refuses to travel with you. He'll stay at a settlement and function as a normal settler, but won't leave or respond to you.

This should be moved to the spoiler section too.

If you are on PC, then you can type player.addperk 8428d as a console command to get his perk.

Dam, thanks for spoiling [censored] bro. next time put a *SPOLIER ALERT* so you won't ruin the story for everyone.

Erm, wasn't the prydwen shown getting blown up in one of the E3 demo's? Like, before the game was even released? The op is hardly spoilerific. Some people are a tad hypersensitive me thinks.

Yep. A huge aircraft with the name Prydwen on the side is shown in the E3 Killing Montage, but it is not entirely clear who the Prydwen belonged to in that trailer. That could be a spoiler to those that haven't seen the trailer and who the Prydwen belongs to is another spoiler depending on how far a person is in the game. Someone could believe that it might belong to the Enclave for all they know if they just started playing the game.