DA did nothing in the heresy never existed. According to old fluff they were together with space wolves, racing to Terra, pausing for Russ to conquer a few world's. That is what is being retconned.
Right, so, doing nothing That's what I meant, old fluff had DA and SW do literally nothing of note after Prospero, just wander as if lost, see all the conspiracy theories about DA waiting for victor based on this.
Either way, the armor of space marines are taken care of, repaired, and blessed relics, and the chapters techmarines probably take care of those suits of armor. I would also assume that after a battle, if the apothecaries go and reclaim the Gene seeds, the techmarines are probably out collecting those suits of armor to take back to the armory for repair and recyling of parts. The only suits I would assume loss are the ones where they can't really reclaim and that would be the ones destroyed because planets were exterminated or lost due to losing a war, or sucked into the warp. I think they would recover all they could after a battle, especially if they won.
I'd thing so too, which is why I find apothecary fluff so dumb. How you can have these priceless old relic suit if standard operating method is ruining them with a drill for nonsense reasons every time owner died instead of just taking the plate off? And it's slower, too, unless armour is made of wet paper I really don't see drilling through it being any faster than unlocking a few clasps...