I think the building blocks of life are so common in the universe it might be a case of "easy come, easy go". It wouldn't be surprising if simple life happened anywhere it was given half a chance at all, but one would equally expect that it would die out just as quickly when conditions changed (which they certainly did on Mars).
And of course nothing is ruling out life in the nooks and crannies of Mars.
And of course nothing is ruling out life in the nooks and crannies of Mars.