Didn't Jetstar try SIN-BLR or SIN-CCU some years back and fail?
Anyhow the yields to and from India now are horrendous. Coupled with a plunging rupee and intense competition, all the airlines are in a price war on India-SIN routes.
When Indigo entered BOM-SIN last year, SQ increased its frequency from 14 to 17 weekly and will at the end of the month go to 21 weekly. The prices fell from (all up) US$600, then $500, then $450, and SQ seems to have stabilised at $400 and Indigo is putting out a $350 fare. It was only a matter of time before QF threw in the towel really.
Same for DEL-SIN. Look up the J fares for DEL-SIN, they're about US$2000 return on SQ.
There's a very easy solution to crew calling in sick on India flights. What SQ does is, if you call in sick for an India flight, you will be rostered on the same flight the following week.