If government officials do their job, they should be able to find enough evidence to charge him with Murder in the First Degree. Even if Mr. "Menendez" Schiavo incinerates her immediately.
Murder is the act of killing someone with criminal intent. If any crimes are uncovered which would have been discovered had a new guardian or guardian ad litem been appointed for Terri, then the only way for Michael to marry his "fiancée" would be for Terri to die. Seems to me a very strong criminal motive, one which could also likely be attached to the other members of the Triumvirate.