1391 was one hell of an unlucky car. According to nycsubway.org, this same car got into another accident 4 years later on the yard lead to 239th Yard.
The Canarsie overshoot set (8277-80) was fixed up but it took 11 years.
The R46s that derailed in QBL (5742-45) were fixed in 2 years.
The 46s that derailed north of 125 (6150-3) however, were half written off, with 6152-3 buddying up with AB pair 6206-7 to make a four car train. It probably wasn’t worth it to repair said cars, as the 46s were at the time 41 years old.
If 207 can fix 1391, the Canarsie set, and the QBL derailment set, IMO they could fix 6346-50, at the cost of the set being OOS for a long time (I estimate 3-4 years).
Condolences to the motorman’s family for his death on the job.