Might not be the most likely scenario, but a runaway green house effect is certainly possible.

If a positive temperature feedback loop happened to the earth’s atmosphere we could definitely end up like Venus, where no living thing can survive.

And as engineers we understand that positive feedback loops cause changes in exponential progression. It can be “almost fine” for a while and then suddenly “there’s nothing we can do” even in human timescales.

And it could happen fast enough that humans don’t develop tech robust enough to survive other planets unsupported, so game over for humanity, better luck next time.

I personally don’t think thats going to happen, but to be honest I wouldn’t want to risk it.