Will mats become useless?
Endgame mat prizes are reacting to supply and demand (as are all mats). Mithril for example spiked hard recently. And people are and will always be crafting- be it for salvaging for ectos or equipping twinks or new players working for their first exotic set.
New crafting recipes introduced etc etc.
Take games like wow which has been out for years now. There is still supply and demand for the crafting mats of all tiers. As long as there is a healthy population there will always be a working market.
Thank you for your answer, you eliminated my doubts. Important that the game has a healthy population and there will always be crafting