Re:
They will if we all panic buy or if people buy them up to stockpile and then sell them to users at inflated prices. You've also got to possibly consider inner tubes too.
Depends how many 26ers one owns, how often they're ridden and how often tyres need to be replaced. Also consider how long one can go on riding before age prevents us or if something happens to the bike in the meantime. Based on my current age and health, I reckon I've got another ten years of riding left in me. On the mileage I do currently, I get through a three tyres in 18 months – one front and two rear.
If there's still quite a market for the 26, manufacturers will keep producing them. When the generation brought up on 26ers disappears, then the market will dry up. It might get to a point where the industry gives up on the 26er.
One could also wonder how long will 29ers, 27.5 and 650B keep going too. Another new format could pop up or the 26 could come round yet again.