You don't have a Gone Girl argument if the jury can see the girl's dead body and hear expert testimony that she was poisoned. No body cases rely upon inferences from circumstances to prove the victim is dead, so the defense can at least argue the point to the jury as to whether the inference is reasonable. To that extent, I can agree that the case against BM is not as solid as most other DV cases.
I find the evidence that SM is dead compelling, and once you get past that point the evidence in this case of motive, means and opportunity are as strong as you get, short of a confession.
I don't think LE is relying on any breadcrumbs offered up by BM in making the strong statements about SM's remains they made in the MTD. They believe she is in a remote location in the mountains around Salida - I'm guessing about 10,000 feet elevation. At that altitude in Colorado, the rate of decomposition of the remains will have been slowed quite a bit. LE may well be able to detect tranquilizer or other drugs, and external evidence of injury, choking, etc. If she's in a container, that could be linked to its owner.
In sum, finding SM is not necessarily "just finding the body." It's finding a treasure trove of evidence that may, in itself, be sufficient to refile the case.
And I bet LE has trail cams all over that place, and along the access routes leading to it.