Can I just point out that there is no need for new negotiations to take place with music rights on "The Muppet Show", let anyone *any* TV show. Music rights for broadcast will have been negotiated back when the programme was made, and don't need to be renegotiated. It's only for commercial release that you (may) have to renegotiate music rights.
"The Muppet Show" was originally a syndicated television show. It has never appeared on American network television in primetime. That was a different, higher pay tier for all the performers, especially the guest stars. No one was paid Network Primetime scale for the show. It's a union issue. Also, television, prior to the home video market and the cable TV explosions, was notorious for not negotiating rights past the initial run and re-runs and certainly never included language like "in any and all media, whether now known or hereafter developed". So if Disney wanted to air "The Muppet Show" in primetime on ABC (which would be a "commercial release" since ABC doesn't own the show, Disney does), they would have to negotiate primetime level contracts with the performers, musicians, probably the directors, and certainly the guest stars (btw, did you know that 11 of the 24 guest stars from season two are dead? So that's negotiating with their estates) because the original contracts would not have included a provision for it.
They would also have to renegotiate the music license rights with BMI or whoever currently owns the rights to the music since an American Primetime Network broadcast probably wasn't included in the initial license.
First run syndication was the redheaded step-child of television in the 1970's. It wasn't until the 1980's that first run syndication was considered a profitable endeavor (thanks in part to "The Muppet Show" as well as "Star Trek: The Next Generation", "Oprah", Wheel of Fortune" and, ugh, "Baywatch").
Rights in film have always been in perpetuity and eventually included the
"any and all media" line.
But hey, maybe licensing issues are different in Lew Zealand.