Does Sneak Attack's ability let you keep the creature if it gains indestructible before end of turn?

Sneak Attack reads: 'At the beginning of the end step, sacrifice that creature.' This is a sacrifice effect, not a destruction effect. Indestructible (CR 702.12) only prevents a permanent from being destroyed — it has no effect on sacrifice. CR 701.17 defines sacrifice as moving a permanent from the battlefield to its owner's graveyard, bypassing destruction entirely.

Even if the creature gains indestructible before the end step trigger resolves, the sacrifice will still occur. There is no game mechanic that prevents a creature from being sacrificed unless a card explicitly says so (e.g., 'can't be sacrificed'). Indestructible is simply not that mechanic.

The end-step triggered ability from Sneak Attack is mandatory — there is no 'may' involved — so the controller cannot choose to avoid it either. Once the trigger resolves, the creature goes directly to the graveyard regardless of any indestructible status.

Example: You use Sneak Attack to put Emrakul, the Aeons Torn onto the battlefield. Even though Emrakul has protection and is legendary, if it somehow also gained indestructible, the end-step trigger from Sneak Attack would still sacrifice it. Indestructible does nothing to stop that sacrifice.