Imagine if someone messing around with hashes accidentally came across two inputs to SHA-256 that produced the same output. Not a concerted effort, not Google/NSA or crypanalysis. No tin foil hats. Just random chance in say a high school. And they made the two inputs public knowledge. Whilst highly improbable, not mathematically impossible. And just that one collision.
What would be the implications? Would people simply say "Well it had to happen someday" and carry on as normal, keeping the hash as is? Or would SHA-256 have been "broken" and an upgrade sought?
An answer to Are there any well-known examples of SHA-256 collisions? suggests that it would be major. Even if it happen entirely by chance?