Sounds like they're struggling to let everybody in... Chick telling us they're opening the lower tier of the South Stand as we speak, with loads still outside...
If the full programme doesn't show up on Listen Again (and it doesn't look like it's going to, for some reason), an edited version might well show up on the Sportsound podcast page tomorrow.
STV seem to think the replay will be going ahead regardless:
http://sport.stv.tv/football/scottish-premier/dundee-united/235350-call-ups-wont-affect-dundee-united-and-motherwell-replay-date/
Exactly what I thought last night. You can't really disallow the sort of goal fans pay good money to see. But anywhere else on the park, and (as you say) quite possibly if he'd missed, it's a free kick.