Well, I'm still enjoying the show and so is most of America, judging by the ratings. Next year is a given now if everyone signs back on for another year.
Well... Segel seems pretty fed up with the show so who knows.
However recently Patrick Dempsey / Dr. Sheppard from Greys Anatomy stated that he wanted to leave Grey's after 8 seasons but considered otherwise when he thought about having to look for work again... a well running show is a steady paycheck after all.
Some of the Mother cast may feel the same even if the show became stale.. work is work even if your heart is not in it anymore.