Yeah, but the life he imagined could have never happened, since Caska loves Guts.
I'll admit that there are some devious circumstances in the way, but fate had set it up just right so that there would be no way Griffith could refuse. Griffith's entire existance was shattered, so of course he would choose his dream of grandeur over protecting his "friends" and living a shattered, worthless life. But it was still his choice, I beleive one of the demons specifically told that to Guts, that if Griffith had wanted to he could have avoided it.
Look at all my trials and tribulations
Sinking in a gentle pool of wine.
Don't disturb me now, I can see the answers
'Till this evening is this morning, life is fine.