I don't know whether or not they are engraved but I would have thought there would be spare medals. I think relay participants who are not part of the medal-winning teams but have helped in the heats are awarded medals and they can't be sure how many teams will use such tactics. I'm not sure about it but I've heard it mentioned by commentators (so it could be wrong).
For what it's worth, I don't think the high-jumpers were necessarily being quite as Olympian and altruistic as people have enthused about. Agreeing to share a medal (at your own, not the official's suggestion) could easily have been a way of avoiding the other athlete beating you in the jump-off. This way no-one has to settle for silver. But I'm still glad it happened. I'm not so sure it'll be allowed again. But it might, because both jumpers had identical records and jumped as high as the other. I think a jump-off is not in the spirit of the thing, even though it could be argued that the medal would go to the most consistent jumper. As they go down in height till one fails, the silver medallist would have failed a height he had already cleared in the competition.
