They are already disappearing and have been for many years. A certain amount of people are completely comfortable already buying stuff online and don't use their LBS's. Perhaps if they go to their local shops to try something on before buying, then a certain percentage of them might just buy from the LBS since it's in their hands now.

Even if they don't fork out the potential $300 that a helmet might cost, they might buy a water bottle holder or pair of gloves while there.

If LBS's ostracize people browsing and just trying stuff on, then they'll definitely be out of business.