Headcanon 1: The mane six turn into /invulnerable skeleton warriors/ when they die, because of their connection with the elements of harmony/tree of harmony/whatever. Only Equestria's mostly peaceful so basically nothing changed.
Headcanon 2: This pic takes place during like Season 5. I'm imagining the fight with Tirek went /really south/ so like all the mane six (except Twilight) are dead. But since they're like immortal undead cartoon skeleton ponies, absolutely nothing changes.
Headcanon 3: Rarity's banned from access to rhinestones and hot glue guns. She finds them anyway. Nobody knows how.