Board Thread:Questions and Answers/@comment-27035013-20151101122706/@comment-11051098-20151105171013

If you compare Yhwach/Jugo to Aizen/Gin, Gin had a hundred years with seemingly thousands of opportunities to kill Aizen, although he was forced to wait who knows how much of that time to learn how to counter Kyoka Suigetsu by touching the blade. He protected Aizen at least once when Hiyori attacked him in rage, and eventually did he attempt to kill him after a century, but in his case it was too late.

The situation is different with Yhwach and Jugo to begin with, though, since Yhwach's power becomes Jugo's to watch over while he sleeps. I assume he becomes The Almighty since his eyes gets 3 pupils and irises.

Jugo could theoretically use The Almighty to kill Yhwach while the latter is asleep, but the fact he has not done so seem to prove that he is completely loyal.