The previous owner did a bang-up job destroying about 1/4" worth of threads on some forks I have. It's not at the top though. It's about 1/4" down, so the top threads and bottom threads are still good.

Anyone know if this can be remedied? Or do you think I'd be best just leaving it since the lock nut should be able to be tightened down and hold the headset in place?

You could chase the threads with a die if they are not too bad. If they are that bad you could have a weld bead ran in that area and then chase/tap the fork.

If the bad spot is far enough down that it doesn't really get into the upper race or locknut you can just leave it.

I have a set of Landing Gear forks that someone rode around loose and damaged the threads. It was far enough down that it has been fine just leaving the threads alone.

I have fixed many sets of forks with tooling I made. I can only fix the type that are sleeved at the base and welded underneath, but basically I can replace the steerer and reweld it in the factory location. This is the best method I have found and I've tried many others.