Your creatures will stay indestructible and you will not lose the game if you are able to prevent the end step of the extra turn from happening.
The effect of Chance for Glory has three parts:
The first part of the effect gives the creatures you control (on the battlefield) the Indestructible ability. This is a permanent change to those objects.
The second part of the effect creates a new Turn after the current turn that the controller of this Effect will take.
The third part of the effect creates a delayed trigger. The trigger refers to the turn that was just created.
603.7b A delayed triggered ability will trigger only once—the next time its trigger event occurs— unless it has a stated duration, such as "this turn."
If that extra turn never happens or never gets to the end step then the trigger does not fire and the effect does not happen.
10/5/2018 Creatures you control gain indestructible indefinitely. If you find a way to not lose the game during your next turn, they’ll continue to be indestructible for as long as they remain on the battlefield.
9/22/2011 If Sundial of the Infinite’s ability is activated before the end step, any “at the beginning of the end step”-triggered abilities won’t get the chance to trigger that turn because the end step is skipped. Those abilities will trigger at the beginning of the end step of the next turn. The same is true of abilities that trigger at the beginning of other phases or steps (except upkeep).
- Ending the Turn
713.1c The current phase and/or step ends. The game skips straight to the cleanup step. Skip any phases or steps between this phase or step and the cleanup step.
713.3. Even though the turn ends, “at the beginning of the end step” triggered abilities don’t trigger because the end step is skipped.
This is covered explicitly in the rulings for the card, available on the Gatherer page:
Creatures you control gain indestructible indefinitely. If you find a way to not lose the game during your next turn, they’ll continue to be indestructible for as long as they remain on the battlefield.