I didnt want to get too cute with the answer but there arent a lot of details provided, so I do make some assumptions.

1. There is gravity on the planet (clearly because it has mass and a given escape velocity)
2. There is matter in outer space that will have gravity

The speed exceeds the escape velocity so greatly that I will say that the rock will land inside some mass in outer space after which the speed of the rock will be:

A) Zero