Well, as do many people out there, I greatly dislike the idea that Demigod could be made better by becoming a DotA clone.
However. *twitch* (Dear All-Father, will I be flamed for this) I think that when a player leaves, rather than leaving an AI behind (clearly a punishment to their team, as the damned thing desperately charges towers for who knows what reason) it may be fairer to remove the person's demi, and refund a portion of their gold, maybe around 50%, to the team (by selling the leavers items, DotA teams do achieve just this on a regular basis). The team's gold per second would then take a slight increase to compensate for their loss of a player.
The negative sides of this are clear enough, I suppose. It may cause the more ignorant members of the community to try and get their teammates to leave if they ever do anything wrong, and it would lead to demigods who were substantially stronger on one team than the other. However, it would definitely be more balanced than the current "Well, sorry mate, your teammate left and all we have is SuperFeeder, who has the power to buff your opponents! *insert AI here*"