yeah that scene was awesome
Sion:I don't need you anymore! *ignites lightsaber*
Nihilus: *random sith language* *Then proceeds to wipe out the room*
Sion: D: ok then *limps away*
Ontopic, yeah I do think sith can use sever force but they cannot use wall of light.
I remember watching the scene on Youtube for the first time, it was sweet. Sion didnt have much of a chance. I think Nihilus was merciful in letting him go.
The use of Sever Force by the Sith is rare. Not many use it, but why Sever their connection to the Force when you can just kill them?