Playing a redemption story with a paladin is fun, but sorry a "roll and you your god is pissed at you" is a shitty redemption.

I've ran several over the years, and they all started with a discussion with the player on IF they wanted to do it, and how they wanted to do it.
I'd often throw in moral dilemmas for paladins in my games, but the choice would always be with them.

Once I threw out a dilemma that had my paladin player retire his character in order to maintain his faith.

The Paladin (level 15 famous throughout the land, his god one of wisdom, compassion and forgiveness) and the party encountered young girl who was the survivor of a village they'd recently passed through in which everyone had died of plague.
This plague was a divine curse (for long running reasons I won't get into), so remove curse/cure disease didn't work.

The players knew that they couldn't get close as they'd encountered the plague before been infected and cured themselves, but they were not immune to reinfection - and so they knew the girl would die, but it would take at least 6 months (the younger the person the longer the gestation period, and the more infectious during it).

So the party, keeping their distance start to decide on what to do with her - they can't leave her, she'd spread the plague to any unwary travelers who might encounter her, or if she made it to any villages. They couldn't take her anywhere for treatment, there was no treatment, and even divine intervention (or archmage level magic) only had a 50/50 chance of cure. They didn't know of anyone or anywhere they could take her that wouldn't result in anyone near her dying.

So they started discussing humane methods to kill her. Poisons or spells they might use (sleep, etc)

At this point the paladin walks over, picks up the girl and starts walking back in the direction of the village. He has the party leave all their food and water, post plague signs around the village - and he stays with her.
The girl dies peacefully 7 months later, the paladin a few weeks after. A temple to his god is constructed at the village a few years later and he is immortalized as a saint - a statue of him and the girl serving as the temple's altar.