Let's look at this deal another way:
Torres stays and becomes not only an all-star shortstop but also has a long hall-of-fame career. That is the best case scenario for Torres. Chances are great that it will be much less than this.
Having a hall-of-fame player on the Cubs is certainly a wonderful thing to happen, but compare it to this:
Chapman is a part of the 2016 Cubs winning the World Series.
Suddenly, Epstein is a shoo-in for Canton (probably considered the best MLB executive ever), Chapman's chances of re-signing with the Cubs would be greatly increased because of the excitement of being part of such a historic event, a 100+ year streak (curse) is over.
The chances of the Cubs winning the World Series this year are much greater than Torres having a hall-of-fame career.
Do you think that Torres will have a better career than Sandberg or Banks? And in the end how close did either of those two hall-of-famers (or the other 31 hall-of-famers who played for the Cubs since 1907) get to winning the World Series?