I remember waaay back in the day, like 2002, when the drought was at its worst, Westy was down around 1,500 cfs. This made Skull really tricky. Guys that I know who've been boating Westy since the 70s say its never been too low to boat, though that may just be a matter of perspective...
As for the flows we can expect this fall, this is a time for someone to send a PM to Kara Lamb of the BOR. She should have a good handle on what the expected releases will be from Green Mt. Res.
Another place to check will be the NRCS flow forecast website:
COLORADO - DOTSERO, NR (EGLC2)