In trying to remove the antenna connector pin from its socket on the airport card the socket came away from its location on the airport card completely, together with the cable and connector pin. Rather than replace the airport card (that would have a new socket) and a new connector/pin for the cable, I decided it would be worth trying to solder the connecting pin to the (now exposed) contact points for the socket on the airport card.
Best time to do this is during the re-build _after_ replacing the hard drive, when the antenna is still unattached to the airport card. After the re-build (with no further problems encountered) it was quite easy to solder the connector pin with attached remains of the socket to the airport card's contact points - there's enough space for easy solder access without other sensitive components nearby.
I had thought that my Mac Mini's wireless connectivity might be affected, but it wasn't.
Now very happy with a fast SSD machine with wireless connectivity.