Actually, Michael's girlfriend is divorced, so that kind of blows the whole idea that he couldn't get a divorce and still have a church wedding out of the water.
More important than that: the Catholic Church explicitly forbids the denial of food and water when such denial will cause someone to die of starvation or dehydration (food and water may be removed from someone if such removal will not cause them harm becaue they'll die of something else first). Consequently, in the eyes of the Catholic Church, Michael Schiavo murdered Terri. Whether or not civil authorities ever charge him with a crime, the church will see him as a man who murdered his wife.
Further, the Catholic Church explicitly forbids a couple from getting married if either the bride or groom has murdered, or conspired to commit the murder of, the bride or groom's former spouse. Since Michael murdered Terri, he is forever inelligible for remarriage.
BTW, one thing I don't know: if a couple that is inelligible for marriage deceives a priest into marrying them, can the Church involuntarily annul the marriage on the grounds that it was never legitimately entered into? Anyone familiar enough with Catholic Church rules to answer?