Not sure why people still lean on the 'Conan is never-ending' theory. I could see the movies and specials continuing after the end of the manga series as long as Conan's a huge draw, but surely Gosho is enough of a professional to give the fans a satisfying ending for the manga.
I'm going to say that the rum arc will be the last arc until the big climax.. which would bring us to about 6-8 more years of this series. Hard to imagine Gosho going into his 60's with the same 3-hours-a-day sleeping schedule writing Conan.