Oh please ZeroX2. It's obvious from your posts that you have no clue of some of the finer points of the gameplay mechanics as they apply ingame. You trying to tell me to learn something is a sick joke.
What'll stop the LSer from running away? Wrong question.
Here's the right question: How can I damage him as he's running? DS has the perfect tools. How about Grip? How about Lightning? How about Drain to make sure they aren't getting Force back and you're getting massive amounts of health back? All three are quasi-area of effect attacks, which LS does not have at all.
The point is that no matter what you do against a good Dark Sider you are going to take damage once your Absorb is up UNLESS you are a hiding god (it can be done, it's just that, as I said, the skill required is insane), and the reverse does not necessarily apply if you are a Lightie due to a lack of consistently damaging long range attacks except for Pull Throw, which takes around 40-50 force per shot. Once you do it twice at max your ass is up for a Lightning-delivered roasting or PT/GT-Drain combos.