This is potentially a masterstroke by Armstrong, of course.
Keep fighting, and run the risk that it will all come out in the wash. Quit now, and no evidence will ever come to light, as he won't be suing anyone, won't be in court, won't have to say the words "I didn't use drugs", as opposed to...
The thing is, he may not have failed tests, but we all know that the users are always a step ahead of the testers. There were drugs in use previously that weren't known about or tested for, masking agents used, and things like EPO/blood doping which wasn't on the radar at that time.
We'll...