If the permanent that was turned face up is no longer on the battlefield when Sumala Sentry’s triggered ability resolves, you’ll still put a +1/+1 counter on Sumala Sentry. Similarly, if Sumala Sentry is no longer on the battlefield, you’ll still put a +1/+1 counter on the permanent that turned face up.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.