I agree with what others have suggested: if you are true-to-the-ideal Mustachian, then having a major windfall is basically pointless. It's the mindset where happiness is already (1) maximized and (2) derived almost entirely from non-material things. If those two conditions are met, what will more money do for you? I think the real MMM (the superhero persona, not necessarily the man who writes the blog), might actually find such a sudden influx of money stressful: it's a new "job" (figure out what to do with it).
While I can easily recite the ideal from rote, I'm hardly there. :) I suspect few are born with it, and for many (most?) that internally-sourced, overwhelming happiness is a skill that has to be developed and nurtured. But it's not a hard skill like welding or a foreign language that can be taught, it's more like a "spiritual" skill. It's certainly a change in fundamental thinking, if nothing else. How big of a change this mindset is and how much care and feeding it takes to achieve obviously depends on the person.
But I also see the "compromise" or "escape" version of Mustachianism, where the end-goal lifestyle may not be the dream/perfect one, but better than working as a wage slave. But even this state I think has some working room. E.g., endure the crappy job just long enough to establish sufficient FU money, i.e. not quite FI, but enough of a war chest to walk away from the lousy situation. Maybe another job is found, which doesn't afford the same pay, but is at least semi-enjoyable. This alone ought to re-frame the end-goal. I.e., maybe the original thought was for life to be just "1 better", but simply taking a non-suck job alone is "1 better", and that makes one realize that life can actually be "2 better" or "3 better" or even "1000 better". And the march toward "true" Mustachianism continues.
I naturally tend to be someone who doesn't desire much in the way of material possessions or even travel, but I tend to struggle more with the (financial) security aspect of the MMM lifestyle... so if I received this magical post-FI windfall, I'd probably beef up my accounts; I'd buy more (perceived) security, like an annuity or TIPS ladder that alone would cover all my family's expected expenses.
Side note: in case anyone didn't get it, my "two chicks" comment above is a joke, a reference to the move Office Space.