After winning...

I always figured that Monty really did hate money now. As a result he would have Spike be his guy who he could trust to handle all the business stuff. but they would go with Spike's original plan to get a cabin and go fishing. Maybe at some point he'd buy a minor league ball team, or if nothing else work in baseball somehow just for fun. Either way I think he would enjoy life without much money, maybe going so far as to keep the fact he is still filthy rich a secret.

Sometimes, Just Sometimes, the joke's on you.

Probably he continued using Jake as his photographer and the Yakov Smirnoff character as his chauffer. He would still pay them the same and they would know that he wasn't wasting money. He would still have the David Wohl character helping him invest his money in different things and he and Spike would certainly stay friends.
I think the whole idea was that Rupert didn't want to just give him money and have him not use it wisely. So at the end, after being forced to spend all that money secretly he would never want to do that again. He would be happy to invest and save and not blow it all.