Can the Jewish People Wait Beyond The Year 6000

We’ve been in Galus for nearly 2k years. We’ve suffered every kind of human suffering known to man throughout this journey. The majority of us have either been killed or forgotten who we are. A small remnant is still holding on, waiting for the day of return. Most of us believe there needs to be some maximal cutoff date when we’re redeemed, we cannot continue like this indefinitely, another 2k years. That cutoff date to this suffering is the year 6000, that’s when the days of Olom Habah begin, as the 7000th year begins The time Shabbos for the world.
Then I heard a recent shiur by Rabbi Zev Leff on this topic, where he states that Rambam in Moreh Nevuchim writes that the halacha doesn’t follow the opinion that the year 6000 is the absolute end date to galus. We have no end date.
My question is, how widespread is the belief in the year 6000 as the end in the Rishonim & Achronim?
What would Judaism look like in a post 6K world with no future date to look forward to, according to Rambam if Moshiach hasn’t come?
Why has the year 6000 been mentioned so much if Rambam doesn’t recognize it?