I would say that in our line of business it’s not a black and white situation and more info on the scenario is required!
However, as a ‘starter for 10’, if you had the facilities and capacity to affect a radar handover then, with a jet with u/s IFF (I’m assuming no Mode 3/A or C?), you should have attempted to do so. Also, unless the transponder went u/s immediately before he was about to leave your freq, you shouldn’t really find yourself in that situation as if you don’t have time to sort out the issues, give him to the FM. (Or were you the FM?!!) However, if you couldn’t get through to the other agency, you and the FM were maxxed with other ac, your ac with the u/s IFF wasn’t hurtling towards other agencies’ traffic and the traffic situation in the vicinity was quiet, (a lot of proviso’s there!); then I wouldn’t have a problem with it. Generally, if you would have been happy on the receiving end of that free-call then that’s probably a good indication of whether it’s good airmanship or not. Overall, without the full scenario, I’m thinking that it’s potentially not the best of airmanship given the environment we work in.
There you are, just what you didn’t want, another smart assed FC answering your question!
Regards, ADIS