Collectors markets only die out when supply exceeds demand. Then, the product loses value.
I have been a collector of many things (baseball cards, beanie babies, stamps, coins) and I have to say that once hype dies down and products flood the market then price drastically changes. Beanie babies were rare because you could never find them in the mid to late 90's. When they came in they would be gone immediately. Now, they are worthless because TY flooded the market. The only way price stays up is if the product is rare and scarce.
Discs are an interesting thing to collect, because they have a purpose and that is to throw. So, they will always have a demand within disc golf communities. But, really once the production ROC3's come out, I am sure that demand will wain and prices will drop down. It was crazy to see prices drop so drastically once the big birds came out and more and more stock was available. Prices went from 200 to 40-30 within a week. I don't expect prices to drop to 15.00 because the limited run of the BB's and Protos, but it should level around 25-30 which is fair market value.