Sci-fi scenario: We find evidence of microbial life from billions of years ago, when Mars was briefly a warm, wet place. Decades hence, a researcher realizes that Mars still has microbial life, but that it has evolved as its environment has, so it's as arid and rarefied as its present atmosphere, wispy and almost not there. Sadly, she realizes that human activity has already doomed it to extinction.
Alternative dystopian scenario: we eventually find evidence of (sometimes extinct) life on all planets and moons that had encountered specific chemical conditions for a long enough period of time. We realize en masse (more than we realize now) that life isn't a unique snowflake, but simply a geological process, not that far removed from rocks and volcanoes. The realization causes a broad spiritual/existential crisis and irreversibly changes human culture, mostly for the worse.