If Flavor Disaster is no longer on the battlefield when its second ability resolves, use its power as it last existed on the battlefield to determine the value of X
If you counter the first triggered ability or otherwise remove it from the stack, it will just trigger again immediately if Nine Lives still has nine or more incarnation counters on it
It's the same with video games, we think "oh this was a great game" than we install it and instantly regret doing so
(Remind me when Worldwake is public and I'll tell you about it.) One of things that is very subtle about planeswalkers is how we try to craft their abilities to match the kind of wizard each of them is
Of those who tried in the past, no one really got it right
(Perhaps both function as a precursor to 2026s planned Star Trek Universes Beyond set, showing us how Magic can handle sci-fi elements?) Edge of Eternities is among the years best, but Aetherdrift is among its worst