The delayed triggered ability will exile the token at the beginning of your next end step unless Sauron, the Necromancer is your Ring-bearer at the time that the ability resolves. If Sauron, the Necromancer leaves the battlefield before the delayed triggered ability resolves, that ability will exile the token, even if Sauron, the Necromancer later returns to the battlefield or you control another copy of Sauron, the Necromancer as your Ring-bearer.