The owners have the right to do sell the bikes and collect the cash. They can spend it for anything they wish - to start a new venture, to enjoy life, to light it on fire, whatever. That's the deal they entered into when they chose to become the owners of this collection.
It's no different than if an individual sold a house or a baseball card. They can spend the cash however they like.
While true, I don't think anyone has ever been prosecuted under this statute for performative burnings. From what I could find prosecutions seem to be concentrated on fraud.
Yes, the internet always struggles when registered nonprofits with what must be millions in assets “go under” in ways where it is unclear what is happening to the assets.
It's no different than if an individual sold a house or a baseball card. They can spend the cash however they like.