I contacted Applebee's after they took their amazing Jambalaya Pasta off their menu. I learned two things: it is probably gone for good, and they will never release the recipe. A post on another website confirmed that the sauce base was alfredo-like, and that Applebee's staff would add alfredo sauce to the usual sauce when they were running low on the latter. Months later, I was able to obtain a list of the ingredients from an empty carton of Applebee's prepackaged Jambalaya Pasta sauce (that's right...it isn't made at the restaurants from scratch!)
Unfortunately, I can't figure out how to prepare and assemble the ingredients so that it comes out the way we all knew and loved. If anyone would like to see the ingredient list, I'll be happy to post, with the understanding that if you figure out how to prepare the dish, you'll share your knowledge with all of us.