There's still a lot of assumptions in there. Obviously the best case scenario is that Maxwell tells all. But even with the threat of life imprisonment this is not necessarily going to be the case. She has already denied any knowledge of wrongdoing by either Trump or Bill Clinton. Do we believe her? If she isn't willing or able to fill in the gaps, where do we go? Is there any possibility we will believe anything other than that every single person that we hate who even had the slightest association with him is a vicious pedophile?
there's two conversations here. what the FBI should do, and what we expect to come of it. its the FBI's duty to run down leads, and currently all roads lead to Maxwell. so thats what they're supposed to do. period. but what we expect to come of it? not much if anything. luckily there are a trove of witnesses, victims, and survivors. they're VERY willing to talk. which is why Bondi is avoiding them like the plague in an attempt to cover this all up. even if their testimony was taken behind closed doors the FBI is unlikely to act on it unless they get a capital crime against a known democrat. so again, what they should do and what we expect as a result aren't the same but that doesnt mean we should let the FBI slide.