what happens to an informants testimony when HE gets busted?

Got busted, not guilty, yadda yadda yadda. The DA has offered several deals since arrested. Now the informant, which is by the way their only witness, gets busted last night and today a better deal yet. (just not good enough yet.) The agent who was conducting the investigation has addmitted that he relied completely on informants statements to make the bust. He has testified at prelim that the informant was not ALWAYS within his vision. He did not see or hear anything himself where any buys were concerned except during one conversation the officer said he "might have heard me say something about some qualudes or something". I was charged with possesion of qualudes which later turned out to be acetomenaphin. (Informant was busted for possession of Meth a month before I was and made a deal. That's how I got busted. Last nite he and his girlfriend was busted for Meth with intent and possessing a precursor to meth.) Question is: What happens to informants testimony now? Is it thrown out as unreliable? Is search warrant valid if the only thing leading up to it was the informants statements?
help izabella