It is online at the Sun-Times (I just caught this on Hardball): Sun-Times article on retirement
Apparently the recently discovered brain tumor has a "dire" prognosis (according to Novak), so he is retiring to face the radiation/chemo required for treatment.
I know that most of us that frequent DKos don't find his point-of-view to be very similar to ours (and maybe quite offensive at times), but at least I never wish any sort of pain like he is likely to face on my enemies, let alone my friends.
It is quite the coincidence that two of the most prominent Washington figures on opposite sides of the political spectrum face a very daunting disease. My prayers will be with him (as well as with Senator Kennedy).