In fairness more than likely the players stayed in Southampton overnight rather than make the trek from Swansea at 8 or 9 am or so. By all accounts the Darling problem was only reported this morning so if they did stay overnight then yeah the hands would have been tied in that respect.
Saying that though clubs usually bring a few reserve players / youth prospects on such journeys to give them exposure and in case of any unexpected injury issues cropping up.
None of that excuses the overall team sheet though, by all accounts the only defenders in the squad for the game were one centre half (Darling) and five full backs (Christie, Tjoe-A-On, Naughton, Tymon and Key). To not bring any centre half (even if its an u23's player knocking on the door) was folly of the highest order.