I speculated last night that there would be an attempt to keep him alive long enough for a transition to take place. Someone has to be in charge to avoid the appearance of weakness that the Palestinians would try to exploit.
Looks like someone leaked that Sharon was brain dead too soon.
On another thread there is speculation that Sharon is being kept alive (assuming the situation is indeed hopeless) through the Sabbath, as Jews are required to bury the dead within 24 hours. Prepping for a state funeral couldn't be done during the Sabbath, thus the need to keep him on life support. Sounds like a plausible explanation.