I have often posed the following puzzler: "Name as many players as you can over the past 25 years who were acquired in a deadline deal (made by any MLB team) who turned out to be All-Star caliber players in the bigs?" Usual reponses include (1) Jeff Bagwell and (2) John Smoltz. Notice that these deals are some 20 years old.
I'm sure there have been other, more recent examples that could be given. But certainly, the normal expected outcome of a deadline deal according to recent history is to obtain either marginal major leaguers (see, Izturis, Ceasar) or a handful of prospects with the ubiquitous "upside", who rarely pan out.
I am in favor of keeping Dempster unless some top quality, Rizzoesque ready-to-wear prospects can be obtained. The Cubs do not need the payroll savings at this point (in fact if they trade Dempster, I assume they will be in the market to obtain free agent starting pitching in the off season, unless their 2013 rotation is to be lead by Travis Wood) and Dempster is likely to have 2-3 good years remaining. Obviously, injuries could occur. But I'm assuming Demoster could be re-signed for 2-3 years at 12-14 Mill per year. I would rather take a chance on a 2-3 year contract for a 36 year old proven starter thanrisk a 7 year contract which would be needed to sign Hamels.