It's true that the manga industry does not end with next week's ending to Fairy Tail. But it may as well have ended. The situation is grim.
First, UQ Holder went from a weekly series to a monthly. One Piece became a twice a month thing. Zettai Karen Children went on hiatus. Hayate no Gotoku ended (as did Bleach and Naruto.) Akame ga Kill! ended. Kiwaguro no Brynhildr ended. Now Fairy Tail.
That was our last weekly manga series just biting the dust.
Of course I'm grateful for series that release once a month. They do have added pages so it's more like they're half as good as weekly series, as opposed to 1/4 like you'd expect. Saki has enough spinoffs that even though it's monthly, it has as much new material being released as a weekly series.
But even among these monthly series, many are on hiatus (like Kimi ni Todoke and Railgun). Many just aren't translated, (like Guyver). Bolt and Dragon Ball Super hardly even qualify, as the anime version is more 'canon' than the manga versions.
There might be 20 new manga chapters from good series in a month now. When Naruto, Bleach, One Piece, Fairy Tail, Zettai Karen Children, UQ Holder, Hayate no Gotoku, Kiwaguro no Brynhildr and Hunter x Hunter were all releasing weekly you could easily have twice as much.
It's also harder to remember what's going on with monthly series. By the time the next chapter comes out, you don't even remember what was happening last chapter, so the enjoyment really goes down. This is especially true when there are random year long breaks because the translators stop, like with Freezing or Sakura Trick.
The routine of reading Hayate, UQ Holder and Zettai Karen Children on Wednesday, followed by Naruto, One Piece and Bleach on Thursday, is all gone. There's nothing to look forward to on a weekly basis anymore. The most recent monthly chapters are just released randomly, whenever the translators get around to them, if at all.
Fairy Tail was the last and the best manga had to offer. When Fairy Tail leaves, the only thing left in the industry is a gaping hole. Maybe if One Piece weren't always going on hiatus. . . But this is where we are. In a week, manga as a whole will become a shadow of its former self. A week of anime will represent more content than a month of manga. That's where we are today.
There hasn't been a good new anime based on a manga source all year, and we've already plowed through 3/4 of all the anime that's going to come out. It could well be that the fall season lacks anything too.
Very recently, it didn't used to be this way. But a week from now, it will become our new permanent reality. Does anyone really think Mashima, Kubo, Kenjiro and Kishimoto are going to create new weekly series that surpass their old ones? Yeah, no. Remember when History's Strongest Disciple Kenichi was still coming out every week? It wasn't so long ago. But the author of Kenichi hasn't made anything new since. He just finished and disappeared. It's the same for all these guys. Akira Toriyama never made anything as good as Dragon Ball after he finished Dragon Ball.
Plenty of new great anime series are coming out based off of light novels. Visual novels are becoming more mainstream and getting more translations than ever before. Original anime projects happen all the time and a lot of them succeed brilliantly (remember Girls und Panzer? Madoka Magica?). It's not the entire industry that's tanking. It's just the manga industry. After Fairy Tail, la deluge.