Over at the Semi-Spew Steve Saideman identifies a second reason folks choosing among PhD programs should not care too much whether Professor X will stay, go (or die). He makes the case for selecting the program with the best coverage over your general interests. Why? See his post for the specifics, but the general theme is: you are young, life is long, and your interests might change (for lots of reasons, one of which is that the person you plan to study with might suck, from your vantage).
Indeed, I am a perfect example. I enrolled in the graduate program at Colorado because… wait for it! I wanted to be a high school teacher. Yup. I went to CU because I liked Boulder (I hold my BA from CU). I knew zilch about the faculty there. And I enrolled in the MA program. I surmised that have an MA in political science would help me land a job as a social studies teacher. Which is to say I solicited the advice of zero high school (or elementary) teachers before embarking on that course. And I moved from Chicagoland to Boulder because I did not like my sales career and though teaching would be better. Go figure.