Nutloose:
I know that was a worry for the crew. The claim is that jump speed, (120kts IIRC), was sufficiently close to stalling that the deployment of a reserve would stall the aircraft.
On the bright side, once someone has done a couple of aircraft jumps the sequence and timing of events and the associated feelings is so consistent that one would very quickly realize that they were hooked up and, like all else in the parachuting, the training kicks in automatically*.
* I really can't say enough about how good basic parachute training was for causing men to immediately revert to training when things go wrong.