Sometimes if my party wants to do something REALLY dumb that I think might be fun, I'll let them "quicksave" and run it through. Players get to attempt the impossible without fear, and I get to TPK without guilt =D
In one of the games with my group we screwed up getting to a heist so badly that 2 of us ended up downed and the other 3 were facing prison. That's when our bard decided to use Wish to try to jump us all to a timeline where our initial plan had worked. The DM let him do it and go back to playing the heist itself.
The DM also used it as an opportunity to reveal some lore, and as we transition to the new timeline we got to look in on some others where the BBEG was winning.
This was 2018ish and we still talk about it. Save scumming can be a lot of fun in the right context.
You could feasibly fit it into the actual lore and make it "balanced" in a sense. The party finds a relic with the power to rewind time by a few moments. Becomes inert for a few days/play sessions after use.
Then there is actually the potential for complete failure (the relic holder dies instantly before being able to activate it), but they still get a sense of safety that propels them into stupid dangerous stuff all the time.
Hourglass of Lost Chances
Wondrous item, legendary (requires attunement)
This magical hourglass is crafted from a strange material, more resilient than steel, yet transparent as glass. Inside, it is empty.
As an action, you can activate the hourglass by turning it upside down and whispering the command word, "Quicksave". If you do, magical sand materializes inside the hourglass, pouring downside for the next 10 minutes. The flow doesn't stop, even if you flip the hourglass again.
While the hourglass is active, you can use one action to turn the hourglass upside down again and whisper its command word, "Quickload". If you do, the timeline is reset to the moment the hourglass was first activated. Every action and even death is undone, but all creatures in all the multiverse retain their memories of what happened, although any creature that was not within 1 mile of you at any point while the hourglass was active experiences this as a sense of déjà vu.
After 10 minutes have passed, or if you use the hourglass to revert the timeline, it becomes inactive, and it can't be activated again for the next 7 days.