Even if one were willing to accept the 'capability holiday' caused by retiring three Jaguar squadrons before the Typhoon can shoulder the burden, there's still the worry about the longer term. Four Harrier squadrons are supposed to serve on until at least 2017, when JSF will START to replace them on the frontline.
The Harrier's can't last that long without spending billions. Using the same pool of Harrier airframes, and hours, to support two or three squadrons would have made it possible, using the Harriers where only a Harrier would do.
Jaguars would have provided a useful means of saving wear and tear on the Harrier, and of spreading the load and overstretch.
The Indians are still building Jaguars and they're estimating a cost of $24 m per jet, with the latest avionics, etc.