Why wouldn't you sell an iPhone this year?
The only time they waited more than 12 months was between iPhone 4 and 4s, but they didn't skip 2011 they just postponed the announcement a few months.
Everyone expects the new phone to be announced in September, a lot of people are still on 24 months instalment plans and are going to upgrade their iPhone 6 and 6+ this fall. iPhone 7 may be a disappointment for somebody, but it will be a good upgrade coming from iPhone 6, let alone more RAM, a faster CPU, 3DTouch and better camera.
It won't be an enticing upgrade for people owning the 6s like me, but that doesn't mean it will be a complete flop.
Maybe they'll sell a few millions iPhone less than last year and will have better sales in 2017, they can survive that.