For a six month closure, it's probably more trouble than its worth to bring the back, but it is an interesting case study. Especially for future outages...
Has alternate trains to Forest Hills been seriously considerded at length? This seems like the no-brainer deal here.
The is prone to screw ups, especially when solo on QBL, as we all know...
If you bring back the , it'd be shortsighted NOT to run it to Brooklyn (Church/18th Av/Kings Hwy). If you scheduled the and properly, you could probably squeeze some more trains as well...