I'd give it a 50 chance of still working. Those old ferrite magnets had relatively-weak spread-out fields. It obv would have affected the whole platter, but the drives/software were pretty good at dealing with weak signals. We had disks, we had magnets and some of us were youngish and bored. you had to be a little persistent to even fuck the disk up a little.

Now, you place a running AC box fan's motor right up to the drive, i'll corrupt the f out of the disk, i did that before.