Filatov was barely 160 lbs soaking wet. Cherepanov also worked his ass off and from what I've read Filatov didn't have the same drive or goal scoring ability. Filatov was supposed to be good but if you asked me after the 2008 draft who I'd take I'd take Cherepanov easily.
You're right though, nothing is guaranteed.
I feel like ever since his death his stock has gone up. I remember there were questions in his season after we drafted him. IIRC he didn't have a super consistent WJC either (though I thought I remembered him winning player of the game once, or maybe that was Sangs).