There's no capability to adjust the trajectory at this point.

They've sent one vehicle, I suppose they could send up a tow truck to repossess it...

There is also the fire extinguisher in the passenger foot-well, spaceman can just use that to correct his course and get to Mars, maybe to wait for the tow truck there...

After the burn was complete they can use the cold gas thrusters to slightly change the orbit (a few mm/s now adds up over hundreds of years)

I heard the batteries were only good for 12 hours. You'd need some sort of power to fire gold gas thrusters.

The final burn was about 6hrs in, so plenty of time then to do any terminal maneuvers (simulating thousands of years shouldn’t take more than an hour)

I think he means adjust their calculated trajectory once the collision occurs.