I didn't have physics in 8th grade,just a science class..
I was a magnet fan as a kid though and did read a lot about them and fooled around with them..never did try the test you mentioned with the iron filings,I suppose its true that two "separate" magnets put end to end with the opposite poles attracting each other could act as one single one though...I figured because it was one magnet broken into two peices,it would act as two separate ones,especially if the glue kept the mating surfaces insulated from each other..
The magnets in question were for the charging system,not the magneto for ignition??..in that case its likely it would still work to produce a charge with a damaged or even missing magnet at a reduced rate,but I think a magneto is much fussier about having everything "perfect" for it to work...
I know the tecumseh I had with magnets that came unglued off the inside of the flywheel for the magneto never did run good after I re-glued them on,possibly not in the exact spot they were intended to be in..I ended up swapping a used flywheel on it that had a magnet casted into the flywheel and it once again ran good..
I tried reading up on how magnetos operate,but quickly got lost after the chapter on "end gap" and all the other technical principles of its operation...I understand the basics,but not the whole theory..