Well if MSEP really is going down, Im guessing the main reason for that is to allow FOF two performances a day which is VERY smart. I have a feeling its going to be very ruff finding a good spot along the parade route for awhile. Having only one 3pm performance would be crazy! Also with Orlando's heat in the Spring and Summer plus these new costumes and dance routines... a night performance will be much easier for the performers!
We can hope that when MSEP does return it will get the Dreamlights treatment, or who knows maybe TDL will give up Dreamlights by then and ship it to WDW, or at least some of the floats. TDL has had Dreamlights for some time now. With them constantly getting new parades and shows I have to imagine a new light parade is in the works sooner or later.
But I think its safe to assume once MSEP goes down, for whatever reason that be, Its going to be at least a couple years with no light parade at MK. Im willing to bet we will see a new nighttime show at MK before a light parade.