Even though Mariah Carey is still well known today, I obviously do not think Mariah Carey is famous as she was in the past because of new young singers such as Taylor Swift and Selena Gomez and more people are looking up to young stars these days. Especially Ariana Grande the singer who recently got world famous, she is often compared to Mariah and Carey and known as "The young or next Mariah" for her ability to sing high ranges and sing like her.
Very few performing artists are able to stay in the limelight for over 25 years, and Mariah Carey is no exception. She has been replaced by younger, fresher artists such as Taylor Swift and Selena Gomez. The younger generation of music consumers simply will not revert back to the old school Mariah Carey style.
Let's face it: popular music is a young person's game. Mariah Carey had an unbelievable run of smash hits in the late 80's and early 90's. She then had a surprising popular resurgence briefly at the end of the last millenium. The Christmas tree lighting performance didn't kill her career. It is just taking its natural course as other younger stars are grabbing the spotlight.
Yes I do think that Mariah Carey's days as a popular performer are over. There is always going to be new performers trying to get their spot in the music and performing business. Many people want to see some one new young and different and that are a breath of fresh air.
Mariah Carey hasn't been the old Mariah Carey for a long long time. But she is still better than most of the so called singers today. At least the note she does sings in are on key. I know it is expected of her to sing some of her old hits live (and of course for Xmas, certain songs are expected), but I think it will be wise for her to sing songs that are more appropriate to her current voice in the future.
While it may be true that Mariah Carey may never occupy the spotlight as much in the future as she has in the past, she will remain for many years to come a popular performer. Look at the careers of big stars like Bette Midler, and you can see that a star of Carey's caliber will be popular for many years to come.