But what did he exactly had to wrap up from before? Only the NM getting rescued and removed the Warlock, but that could have happened in one issue. He had the perfect opportunity to do a character based run, since he had the perfect excuse to use a smaller cast, and also say something meaningful about the franchise, but he chose to go in the exact opposite direction. While Hickman was always taking over, if he did a great job, he surely would have fans want to know what he's doing next, in the X-men franchise or elsewhere.
And I don't think he would benefit from more issues. He seems to be the kind of writer that, if he had, say, 30 issues, he would stick 50 issues of plot there.
That implies a story can only be meaningful if it's followed up by other writers, and it would be impossible to tell a meaningful one in, say, an out of continuity or alternate future book. And, like I said, if Rosenberg wrote a good story that fans loved, he probably would get another chance in an X-book or elsewhere.