Actually, I don’t think Vetinari wants Vimes to be the Patrician. He’s really not suited for it; a politician of that sort really HAS to be insanely intelligent, diplomatic, and able to deal carefully with the sort of moronic nobles and guild masters HV has to deal with on a regular basis. If Vimes was in control of the city, actual CONTROL, doing what he thinks is best, he’d have the city in a revolution within a year.
No, I think Vetinari wants to keep Vimes right where he is. Here’s why.
Let’s say Vetinari dies, or is deposed successfully, or is otherwise no longer the Patrician. Can never come back, sort of thing. Vimes is emphatically not loyal to the Patrician, at least not more loyal than he is to the city. If Vetinari went insane and all Snapcase over everything, Vimes would have him arrested and executed.
I don’t think Vimes is supposed to be the next Patrician. I think Vimes is HV’s ace in the hole. Let’s say…Gephardt Sock is the next Patrician, and Vimes is still Duke and Commander and all that. Vimes has enough power in the city to make sure that Sock doesn’t screw things up too badly. If Sock, say, tries to kill Vimes or take away his power, or if he’s too crazy to live, Vimes will destroy him, even if it means civil war.
The interesting thing is, there’s only a few differences between the two Vs. Vimes is an optimist, he’s not as bright or as well-educated as Vetinari (though he’s excellent at thinking on his feet), he is not naturally subtle or conniving. Vetinari uses people; Vimes never would.
And Vimes doesn’t want power. Which would make him an excellent leader, natch.
And if things got really bad, Carrot could always take the throne…if things got to that point.
whew You can tell I’ve been thinking about this a lot lately. 

