Muzan is great. What better way to live than to avoid the one person than can kill you. Ain't no shame in that. I'd do the exact same thing in his position, lol.
Yoruichi though, man, he had it rough. He knew the consequences of his failure would be far reaching and it weighed on him heavily. He probably spent the remainder of his life trying to find Muzan, but could never again locate him.
It's a shame the First Pillars kicked him out despite his strength, but think about it. Their organization had already spent centuries trying to kill Muzan and the one person who was closest to killing him failed to do so. Not only that, but he let another demon, who, for all they knew, would go on killing more people, go and his own brother turned coat. It wasn't his fault, but from their perspective, he snatched defeat from the jaws of victory.