Agreed, the problem is that in many scenarios where the US becomes a failed state.. you probably want to be IN the US rather than living under our security umbrella (Canada/Europe/Japan/Korea/Taiwan/Australia). Or worse, in a nation we might end up in a shooting war with (Russia/China).
Either enemies are going to make moves in our absence, or we are going to pray upon former allies (next orange man takes his trade wars kinetic).
So I'd rather still be in the exponentially larger (population & land) isolated continental power surrounded mostly by water and smaller states.
If by failure you mean fascist and authoritarian, America could still reach you.