No, no MUCH easier than that. All DA has to do is prove Dale was last to see her alive and that there is no sign that she is still alive. Check out the 90%+ conviction rate of murder trials where there was no body found. Over 300 cases and they USUALLY get their guy/gal...Here they will get Dale! JMO
To further my previous point on this issue, I don't think that convincing a jury that Michelle has been murdered with or without a body is a problem for the prosecution (assuming trial). I think most reasonable people would arrive to that unfortunate conclusion. I think the real problem for the DA's office is to prove that Dale did it (or for that matter someone else), especially if a body is not available that can possibly shed a light on time of death, cause of death, method of death and so on and when there might not be compelling forensic and/or circumstantial evidence to point to DS' guilty. Please note I said might not be, since we know of no such evidence and by the fact that they have brought no charges against Dale 6 months into the investigation (even longer by now). IMO