imdb FAQ board gave the most plausible explanation as to how batman ejected in time before the nuke blast.
remember when he 1st started off, the BAT was flying low and it looked at 1st that it's because the reactor was too heavy? in actuality, it was due to batman setting his coordinates to direct the autopilot where it needed to go! then it began to pull up, blasted at the building, then ejected BEFORE the BAT went thru the building.
the reason why you kept seeing batman in the cockpit till the final is because he was still IN the cockpit which was EJECTED (misdirection).
so he ejected after he blew a hole thru the building, but before the BAT went thru.
remember when he 1st started off, the BAT was flying low and it looked at 1st that it's because the reactor was too heavy? in actuality, it was due to batman setting his coordinates to direct the autopilot where it needed to go! then it began to pull up, blasted at the building, then ejected BEFORE the BAT went thru the building.
the reason why you kept seeing batman in the cockpit till the final is because he was still IN the cockpit which was EJECTED (misdirection).
so he ejected after he blew a hole thru the building, but before the BAT went thru.