I feel like they're going to try and hold out PHANTOM till at least the 30th Anniversary. The numbers during holiday seasons are keeping it afloat, along with the fact that its still doing decently well during the off season.
LION KING has at least another ten years in it. If FROZEN does ever get to Broadway, it might shift focus from the lions to the ice queen slightly.
WICKED I think has a good 15 to 20 years in it. Especially if they make it into a fantastic film.
As others have said, MAMMA MIA is gonna check out within a year. There is no way the theater owners will let them perform to empty houses like they have been.
CHICAGO might close up shop within the next two years or so. Stunt casting isn't really doing the trick anymore.
JERSEY BOYS will probably have another three years added on due to the movie.
THE BOOK OF MORMON definitely has another five years in it, at least. Especially if they make it into a film...which will probably be a massive hit and propel the show even further.
To be honest, I think POTO, WICKED and LION KING are gonna be the long, long runners with BOM being another potential long runner.
"Life in theater is give and take...but you need to be ready to give more then you take..."