I don't think McCabe was getting any kind of sweetheart deal.  Probably a guaranteed jail term of not less than 5-10 years, in exchange for damning testimony against his puppet masters.  Now if he's convicted of treason, he risks a death sentence.  Without his help, the prosecutors will have to work a bit harder to nail them all. I think he's holding out for Trump to be removed from office, but I also think there's going to be a change in the 2020 elections that could work against him.  Just a tiny amount of cooperation from the House and Senate would speed up this process significantly.