Garcia is the forgotten man now and I hope he feels miserable that he kept quiet out of loyalty to Katie. It certainly appears that he was getting all of his information from Katie so that even if he would choose to cooperate, it wouldn't appear that he could say much that would advance the prosecution of the Adelsons beyond possibly corroborating what Katie is going to say. Moreover, adding him to the mix would risk further weakening Rivera's testimony. Obviously, there's no love lost between those two former friends, so I believe the prosecution wouldn't be terribly interested in offering Garcia anything at all at this point.
On flips and proffers,
1. According to Saam Zangeneh (Garcia's original attorney), the SAO repeatedly offered SG a deal. In recent correspondence with SG's appeals attorney, Baya Harrison, Harrison writes that that even post-conviction, the state was willing to make a deal with SG for his cooperation. After KM's sentencing, Tara Kawass stated that SG has even more intimate knowledge than KM of the murder plot. SG may choose not to cooperate, but the idea that the state wouldn't be interested is IMHO incorrect.
2. Saam Zanganeh's post-trial statement about WA/CA/DA ("if I was those 3, I would be shaking in my boots") probably just means that SG told him the story of what happened. SG has never said a word. Were he to speak now, he'd be an outstanding witness.
3. Fancy Fiction just posted that Rivera's proffer was taken 10/4, released to the defense on 10/7, and posted online by 10/10. We will not have to wait to CA"s trial to see this proffer.
4. Prior to a recorded proffer, the attorneys talk, so the SAO already knows in general what KM will say.
On the impossibility of new evidence,
1. It has repeatedly been claimed here that no new evidence can emerge in the CA case, that the SAO would have had to disclose it for KM's trial. However, according to CA's attorney a few months ago, the SAO has introduced an additional 500+ hours of wiretaps into evidence that were not used in the KM case.
2. Close followers of the case who look at the discovery documents (on the "Close Up" account on YouTube) will also notice additional new evidence not disclosed at KM's trial.
New wiretaps and KM's proffer could really change the picture, at present most commentators have been focused on the evidence that was used to convict SG and KM.