That would still leave Yang Kai the ink battleground and the pass between the ink battleground and the 3000 worlds. The ink giants are currently in that pass, the only ink royal lord in the battleground. Plenty of work for Yang Kai to do over there. For example the ink giant and the normal giant are still locked in battle, so Yang Kai only needs to keep distracting the ink giant so much the normal giant can destroy the ink giant. The other ink giant is stuck in place due to the efforts by Smiles and the nameless ninth ranker. Yang Kai could go and try to figure out how to weaken that ink giant. There's no way he would achieve nothing if he spends a century doing it. If territory lords come to bother him, he's free to kill them. If the royal lord comes, he needs to flee, but if he can flee behind the royal lord's back, he can destroy many of the royal nests the ink clan has.
Plenty of work to do.