When you load a savefile, you must also specify a save file for the other main character, even if you decide to start out without him. If you do start alone, the other protagonist will confront and fight you at the end of the tire factory. When beaten, he will drop a usually large amount of money, although in some cases almost no money at all. Now, consider you drop half of your money when you are knocked out.
Slick being a relatively weak Anti-Climax boss at the end of the game in the original NES version makes a lot of sense when you consider he's Alex's weaker childhood friend Simon, who wanted to prove that he was strong.
