yeah the foreign object would be the locking nut on the end of the shaft that has gone!

at the rate it was possibly spinning id imagine the blades would brake up into very small pieces and very easily work there way through your engine..

either way id expect the worst case and deffo get the head off, if all is ok you wont feel as bad lol

get it back to them tho before you mess to much just so they aware of the problem if nuthin else.