Gintama's anime is waaaay to popular in Japan to just end.. The manga itself is in the 6th ranks and the anime is even more popular than that and the DVDs sell really fast. In fact the gintama franchise is the one that makes sunrise the most money.
Also the seiyuu and several of the staff have said that even they aren't sure if the show is really ending or if its just an end trope to make more money for the movie.
Plus its been states recently that since the movie is selling really well and has already reached a (I think it was) billion yen.. That it may come back based on that.
My opinion is that the company just got tired of catching up to the manga and having to stop every half year/year... So this time they decided to wait it out.. Maybe even pull a inuyasha final act and just when the manga ends come back and animate it all..
Since they ended the show with an actual chapter from the manga as and ep instead of making up and ending like most shows its highly likely they will come back.
In Gintama and Gintama', they ended because it got to periolously close to the anime. Gintama' Enchousen also caught up close to the latest manga chapters, so that's probably the reason it stopped. But that doesn't guarantee there will definitely be more episodes, though. There are chances that this may depend on how well the movie sales goes or something, but anyhow, I wouldn't take the ending seriously considering this is Gintama we're talking about.
If you see the last episode farewell shiginami...it says that the shiginami will return...also a new enemy shoyo "gintoki's master" has shown up...so maybe they will do an arch on him...so i would say they will make 1 or 2 more archs to wrap it up in 2017 or smthn
