Buying UO and making drastic changes to it would be a lot worse than leaving it as it is.
People don't like change, and they especially don't like change to things they like.
Your better bet would be to fund development into a new sandbox MMO.
As for me, I'd put maybe 10mil of it in savings, as a buffer, because losing everything is always a possibility.
Less than a million would go towards getting myself a modest place in a nice area (no mansions, no fancy cars, no pools).
Half of what remained would be invested. After personal bills and food, the rest would go to things like homeless shelters and schools.
As for the remaining half, going "all in" is a good way to lose your "all", which means the returns stop, and so do the donations.