Ask Lemmygrad

what happens inside and outside the us when dollar hegemony goes away?

Hyperstagflation for US. USD value will drop significantly crushing America's purchasing power. Combine that with the excessive money printing that US banks are notorious for and you get double digit monthly inflation. (Rich will race to buy up assets like property even more putting housing even more out of reach which has a knock on effect to rents.)

Recession for rest of world as their US bond assets lose value and their export sales to US lose their profitability.

will manufacturing be reshored to the usa? will it usher in a wave of prosperity for the usamerican colonizers?

Doubtful. Manufacturing relies on effective supply chains. The US would be in global competition with other countries that are far more established with far less debt.

.>will it free the periphery from the chains of empire?

Not really. A lot of countries like say Mexico and Canada are inherently linked to the US economy. When US goes does it will drag down plenty of other countries that are too slow to diversify.