I cannot see why they would "fade away". They seem superior to other phones, service is better (they replace if you have a problem), and they update once a year.
Also I am a PC user, however I can still use my I-phone with my PC.
I have 2 friends who bought a generic brand (Samsung) and one actually threw it out after just 3 months and changed to an I-phone.
so, NO, I think i-phones and Apple are becoming more and more popular and will not fade away.
I do look forward to the next I-phone, however as I buy them outright as against a plan, I have no reason to change unless they come up with something really great, which could tempt me!
They will fade away, it's just a matter of when. It probably won't be in the near future, but all technology eventually evolves or dies. If the iPhone is to survive as technology progresses, then the iPhone of the future will look and work completely different than the iPhone we know today.