See, planets don't matter. G0-T0 will never leave Nar Shaddaa, unless he has to inorder to escape. There would be no need to attack other planets. Just wait until your enemy rears their head. He holds the cards on Nar Shaddaa, all of them.
Also, Hanharr wouldn't be bribed. He is loyal to G0-T0 and the Exchange. Correct me if I'm wrong, but doesn't Mira say its because nobody else will hire him? One more thing, your scenario where Urai fights them off, ( is that yours?) whatever is wrong. It would be Hanharr fighting while at the same time, HKs are in hidden spots, and sniping him. He wouldn't survive. They would make HK's definition of love.
But if G0-T0 doesn't leave then how can he destory Tyber's power base?
Tyber can (and does) project power on a galactic stage. The war is all over the galaxy if G0-T0 doesn't leave Nar Shaddaa then Tyber wins by default.
Hanharr won't be bribed? Is loyal to the Exchange? What game where you playing? He (if you are dark) comes to YOU with a plan to find G0-T0 and kill for the Hutt. So yeah, he is not as loyal as Urai.
Also how do picture the fight going down? they walk into an area and some one yells start? I pictured it that either
1. Hanharr arranged events before hand with Tyber.
2. They ambush him with the HKs on point, Urai senes something and slips away. His troops get shoot up and he plays a cat and mouse game picking off the HKs one by one. Then he has a Boss Battle with Hanharr and gets Tyber to convince him join. Also G0-T0s' HKs weren't all that good a fighting.