Do the Event Items and Weekly items stay forever in STW?

I read somewhere that event items are temporary. But it’s weird because who will invest 3200 gold in a schematic that will disappear in a week? Please clarify this doubt.

They are available to purchase for a limited-time item, but once purchased, can be kept forever. The “temporary” nature refers to the fact that they don’t stay in the shop forever. Once you buy something, however, it’s yours forever.