Hop flavor will taper off with time. But you'd be surprised how long it will last for. Just the other day there was a guy that left his beer sitting in the secondary for, get ready for this, 10 years. He found it and was like, "Oh yeah, I was making beer a decade ago". He added some yeast and bottled it anyways. It turned out just fine.
As long as the seal on the bottle isn't broken, it will last a long time. Really high alcohol beers, think barleywines, can even develop new flavors with years of aging. I personally have opened a bottle of my fathers beer that was 30 years old. It wasn't anything to write home about, but it was still a drinkable beer. Of course, it probably was never a great deal better than that anyhow. (My father tended to use lager yeasts fermented at saison temps)