The next biggest economy would likely fill the power vacuum, which at the moment would be China.
European countries with likely band together but still align their policies closer to Russian polices because they’re a more imminent threat than China.
There would probably be several small brush wars as countries try to to consolidate power amongst regional areas like North America and the Middle East.
Fragile ceasefires backed by American influence would pretty quickly dissolve like between North and South Korea.
And in a few decades everything will settle into a new “normal” just like it did when other great empires have lost their influence.