Im sorry to say but people do not you owe you anything. Just like game developers are not owed to stay in one project. These people most likely want to stretch their wings and gain experience working in multiple projects and it happens to a lot of developers in the field. What about us? In many of the interviews Yoshida has always expressed how he always wanted to be the producer to one of the main FF games. FFXIV was just handed to him and inherited a lot of its legacy and problems. It wasnt a project of his yet he stuck with it because he wanted to make this game good. Now that he has, he would like to take his crack on something he can create from scracth. FFXVI is his chance for that. And he also has gone on record that he would like to produce one more MMO before he dies (perhaps the 3rd mmo for the FF series?) so gaining experience in the field is always good for the developers, rather than staying stuck with one thing is usually not very good in the long run. You'd get burned out.
And even then you guys are acting as if he's just gone. He's still managing this game, despite people believing that its quality has deteriorated.