So the current versions of the AIM-120 have the ability to hit their target without ever going active?
It would seem like that would give an aircraft such as the F-35 a good ability to improve the missile's Pk (whatever it may be). Since an aircraft's radar only scans a maximum of 120 degrees around the nose of the aircraft (and earlier radars have an even smaller azimuth), and an IRST system scans a much, much thinner region, if the F-35 manage to find the opponent aircraft before it finds them, the F-35 could maneuver into the 240 degree region around the aircraft not being observed by the IRST or radar (some Russian aircraft have backwards-looking radar, but that would still leave the sides of the aircraft without any kind of sensor besides ESM). In that position, the F-35 could fire the AIM-120 and use the datalink to guide it to the target. The F-35 uses an AESA radar, and because the AIM-120 was guided by a datalink (and because the datalink currently being developed for the F-35 is LPI), it wouldn't use its own radar, so the chances of the opponent's aircraft's ESM systems detecting either the aircraft or the missile would seem to be very low.
In this situation, both the aircraft and the missile wouldn't be detected -- the F-35 would detect the opponent's aircraft before it detected them (it would probably have a good ability to do this because of the DAS), and would maneuver into a position where both the aircraft and the AIM-120 wouldn't be able to be detected by either the plane's radar or IRST/thermal missile launch warning system. Furthermore, because the only radar in use would be the F-35's AESA/LPI radar, the opponent's ESM shouldn't be able to detect either the aircraft or the missile.
In this situation, it would seem like the opponent's aircraft would have no knowledge of where the F-35s were, or that a missile had been fired, until the AIM-120 detonated... this would give them no time to evade the missile, electronically attack the missile, or attempt to deceive the missile by either firing chaff or descending to a location with significant radar clutter.
Of course, that's all just my speculation. Is that sort of situation actually possible or feasible, or is there some gaping hole in my reasoning?