One, you need more to a post than just "look at my title." Two, I see no reason for there to be 17 wrecked Penguin UFOs on a planet from me grinding them for the lulz. If you can summon it multiple times, it shouldn't stick around when you kill it.
He wants the bosses to not disappear when YOU die fighting them, so you don't have to keep building the summoning item. I'm not sure I'd like this, unless the boss gets all his health back every you respawn.
But.. they DON'T disappear? Unless they changed that in Angry Koala, but last I checked they don't, just make sure you summon them near spawn so they don't wander off.
I don't know man, I was just clarifying for the previous poster who clearly misunderstood what the OP meant. I know I died a few times messing around fighting the dragon boss and he came back twice, but after the third time he disappeared. I summoned him on a dirt bridge directly over my spawn/beamdown spot.