This is fun to contemplate:

There is a lot of ice frozen into the Martian crust. The heat of an enormous impact would melt a huge amount of it. If, as some believe, there are microbes living deep under the Martian surface, such a burst of warm, wet conditions over a substantial chunk of the planet would give them a brief chance to thrive at and close to the surface before the planet refroze. It’s not obvious how to observe such exciting developments, but there are surely already people at NASA and elsewhere giving thought to the matter. And they will have time. Parts of the surface and subsurface in the impact region, if there is an impact, will stay warm for decades.