Are my heads blown on 924S due to oil cooler seal breakage?

If you never ran out of oil or overheated it, it would be like fixing something that may not be broke. I would say you have a 90/10 chance that you are just fine, fix it and drive it for a couple of weeks then have the mechanic take a review of the engine, that will tell you... you aren't going to damage anything by that isn't already damaged...