So I completed the Battle for Bunker Hill for the railroad. I was holding off going to the Prydwen with Danse so I go there immediately after the battle. We take off, and sure enough you can see Shawn on the rooftops of the CIT ruins. You can also gun him down with the minigun.

As my various quest failures are counting off, I see another Vertibird patrolling. You can gun those down with the minigun as well.

The Boston Airport erupts in laser fire as we arrive and I dismount to a hostile Prydwen and the tolling of even more quest failures.

Totally worth it.