Considering the money he made from Braid alone (let alone The Witness, which back then he claimed that it was about to surpass Braid's sales) - $4m mentioned at some point - i'd say the mistake would be his expenses.
$4m alone (again, let alone his other games) would be enough to retire and make languges, engines and whatever else he wanted.
US is huge, i'm 100% certain that he could move to a cheaper location if that was a concern.
And with the Internet there isn't really a reason to limit yourself to people from US, a fraction of that would be enough to contract people from EU (though i'm certain you can also find people from US with much less than $500k/year-$1m/year to work on games).
$4m alone (again, let alone his other games) would be enough to retire and make languges, engines and whatever else he wanted.