For me, it will all depend on Halo Infinite. I think 343 Industries did a great job developing Master Chief, at least initially. Halo 4 showed tremendous promise for being a game that was finally about somebody specific. The original Halo trilogy was never about the Master Chief; he was simply the plot device designed to be powerful and stoic and witty in order to move the story forward in between the playable bits of the game. But the playable bits, which are a much higher percentage of game time than cutscenes, held literally no development of Master Chief as a character.
Then, yeah, Halo 4 comes along and you have got the broader story about the Master Chief accidentally releasing the Didact and having to escape Requiem to save Earth and that is executed about as well as such events are handled in previous games. Master Chief neutralizes the immediate threat and saves the day. Except Halo 4's secret weapon was the relationship between Chief and Cortana, which was such a successful story to me, as it naturally kept conflicting with Master Chief's (and the player's) duty to kick alien -Yoink- and save humanity. Master Chief and Cortana actively developed the problem in conversation and during gameplay, and it makes it heart-wrenching when delay after delay keeps occurring on Master Chief's personal desire to get his AI friend home to Halsey for some healing. By the end of the game, it is obvious that Cortana is not holding it together, but the way Master Chief consoles and keeps her together for short bursts of time - and she in turn does the same for him - speaks to the importance of their relationship to the Master Chief. But it was also obvious they had wasted too much time and Cortana was not going to make it. The very end of the game did a great job asking a question: Chief sacrificed his want (to save Cortana) in order to deal with his need (to fulfill his duty to protect humanity); how will he navigate this gap in future, after pain on the scale of losing Cortana?
Then Halo 5: Guardians came along, politely pushed the dangling plot threads of Halo 4 off to the side, and proceeded to make us watch six to eight hours of things just happening to action hero characters for no apparent reason, and there was no Halo 4 level of Master Chief to be found - not to mention the Master Chief was hardly even in the game. Yeah, I am going to be annoyed if the Master Chief in Halo Infinite is Halo 5: Guardians Chief levels of bad. I think that if that is the case, I will agree with you that it might be better to delve into different stories, even in mainline installments. But if Halo Infinite can restore the deeper style of storytelling 343 Industries initially dropped with Halo 4, I think it will position Chief to maintain his place at the franchise's center. There are still great stories to be told about this character. If 343 Industries does not pull one of them next, I think it will then be time to say goodbye to our beloved Master Chief - at least for a long while again.