I had a PF grog who would build characters hyperfocused for the the situation they were in, and then as soon as that situation changed, would "get bored" and ask to roll a new one.
I never had that directly. I'm pretty generous with respecing and backup characters.
Generally, between sessions I allow a total respec. This has saved PCs when players got bored or realised a build didn't work how they wanted. Oddly enough, it was PF2 that was the worst for this. "I want to be a pirate that duel weilds" was surprisingly resistant to being made with any kind of effectiveness. It speaks volumes when the party rogue gets out DPS'd in melee by the fighter and even the druid. They were a good sport and kept with the concept it until the end of campaign, but they quit TTRPGs after.
For backup characters, I allow players to roll as many PCs as they like, but only one can play at a time. And in simple games like Knave, I allow multiple PCs to share a health bar and action pool.
The closest I had was a guy who quit a campaign 2 or 3 sessions in. I think they were an elf ranger, but they had a pet spider I remember that much. What was odd was he kept demanded rolls during downtime to see if his spider turned on him. When he failed one, he described how his pet spider webbed up his character during the night, and then he stopped playing. I never saw him again, but I suspect it was some kind of fetish thing.
It could be interesting if you wanted to run a short idea involving a road trip, like maybe something about fugitives. It would depend a lot on what system you're using and how much your players are interested in tracking that sort of thing.
I've wanted to run something like that for a while. Never got the chance. Basically a road trip through a post apocalypse with people scavenging for fuel and supplies. There was some Savage Worlds ruleset (I think it was Hell on Earth Reloaded) that I was going to use. Iirc it abstracts loot into a single "supplies" resource with tables on what they find and where. I even designed a point crawl with different encounters.
The plot was finding a cure for a plague, with the twist being that the "cure" turns out to be a person. The world was a mix of Mad Max and Half-Life 2.