BlizzABS::Processor#remove_summon, this is where the summon is "killed" regardless of whether it actually died or not. Simply alias that method, check if it's HP are over 0, find the item that can summon it, add that item once into the inventory and then call the original method. Just keep in mind that this won't work well if you have 2 items being able to summon that monster.
EDIT: Ok, v2.54 is up.
@Aqua: The animations aren't sizing down because you are using a script that messes up the title scene or doesn't call the title scene at all. Because RMXP is stupid enough to load everything in the title scene rather than upon game load, I had to add the resizing at the end of the title scene. No title scene, no resize.