Of course almost all startups expect a long live, but strategically it may be better (for the founders) to close when the fundamental assumptions are no longer valid, in order to do a future clean restart in a brand new endeavor (usually after a detox period).

Agreed. I think building a startup should also rather have a fast failure in case it doesn't work out. I've seen friends trying for several years, only walking away in the end with almost nothing.

Opportunity cost is very real. Chasing the wrong thing for 5 years can leave you broke instead of pocketing 7 figures gross elsewhere