Hi Lissart,
The worst case scenario is if you go around late with the departing aircraft already past V1. You will not be able to see him once you've rotated, and the gap between you is closing.
If the departing aircraft does reject the take off, the minimum distance between you landing and him being below V1 should not be less than 1500m (at STN). You should be able to land and reduce your speed to below his V1 speed within 1500m, your separation will then increase.
The chance of him rejecting the take off is less that him continuing to get airborne so continuing to land is the safer option.
I tend to agree with most of Dani's posts.