I assume you are running a quill stem. If so, not a whole lot can happen even if it cracks at the rust. You will have the steerer captured by the quill wedge. The stem by the headset race. So the worst that can happen is the top of the fork goes loose. Do your best to stop before all the bearings fall out. Steering might get sloppy and tough but I'm guessing the adrenaline in your veins will carry you through.
More realistically, I'm guessing that fork will go a long, long ways just fine. That spot down low, I'd be concerned. But up there? All the top race does is keep the column in line. Not a tough job. I'd grease the heck out of the threads and spot with marine grease, to keep water and more rust away and to mark it so I remember to look again when I do HS maintenance.
Maybe others will have more concern. We'll see.
Edit: You say this is where the stem was attached. Are you saying the stem was a clamp-on for a threadless steerer? That water got in at the slot at the back and at the bolts? So this spot is above the headset and that if tie steerer broke there, the stem and HBs come off? That would make me nervous. If I loved this bike and the ride, I'd put a quill stem in it (cutting it down if need be) or take it to a framebuilder for opinion and repair.
Last edited by 79pmooney; 07-04-22 at 11:40 PM.