I continue to believe that whatever his motive was (even originally) would determine what happened to her body. If it was insurance money, and maybe even custody of Baby K, I would think he'd want her body discovered (in relationship to a "robbery"). Proof of death would speed up either of these scenarios.
If something went stray with this motive, then, yes, he would have had to come up with another plan...make it looks as it she had left on her own. Again, stupid to do this without also losing one of her vehicles.
If the motive was something else (not sure what), then getting rid of the body as effectively as possible would be the plan. All JMO