I originally had some ideas for this post, and then I saw Drew Brees's book cover on the SB Nation photo thing, and immediately with horror I asked, "What hath God wrought?"
But in all seriousness, I don't think the Saints are going to suddenly drop off a cliff. The reason I say this is because no matter who coaches the Saints next year, it is very likely they will still have Ol' Brees at quarterback, and his past few seasons with Payton at the helm have taught him more than enough to know what plays to run and when. And Carmichael has shown he can call plays as well.
Plus, don't forget who their new DC is. I don't believe anyone has mentioned that it is likely that their D will improve as well now that Spags is their DC. Even if their offensive production falls, we will still have to contend with what will likely be an improved defensive effort from them.
Ideally, they'd fall totally out of the NFCS contention and we'd run away with it.
Realistically, they're still going to be the Saints.