I have to agree with flowbee. I grew up waiting for the day he hit 756. He would be somewhere around 650-700 if he didn't miss nearly 3 full seasons in the latter part of his prime. He has proven that he can hit 35-50 homeruns on a consistent basis, but he can't stay healthy through an entire season.
I think he will end up around 620-650 because I think he will stick it out until 40.
Take a look at how many games he played in 94, 95, 01, 02, 03, 04 and 05. He would be sitting at 700 easy if he played the full seasons...not to mention closing in on 3,000 hits too. However ifs are fun to think about but never get you anywhere.