Re: Can I just cut the cable?
I would say that unless you can disconnect that cable from the splitter that its attached to then just cutting it may cause problems with your signal (potentially, worse case scenario). Realistically nothing will happen but if you can locate where that cable is plugged into then I would disconnect it from there and the cable. Ideally a cap should be placed on the open port of the splitter to prevent ingress.
Is the cable loose enough to pull back into the roof? Rather than cutting it why not pull back the slack into the attic?