Obviously, there needs to be more then just one thing in place to make the chip obsolete. In order to truly be obsolete these things must all take place:

Chips pulled from the floor. (if being used)Redemption notice-
All remaining chips destroyed (numbers documented)
Continued documented destruction in the future if chips happen to come in. I would expect there will be errors by the cage folks, and chips will continue to be redeemed. There can also be chips put onto the tables by players long after a closed redemption without dealers picking up on it.

Documentation of numbers is important. If we know how many chips were issued, and we know that all but 50 were destroyed....we can assume that a maximum of 50 could exist.

WE will always have the possibility of a few boxes of chips sitting in the casino owners basement....or in his game room to be used for a home poker game. There's always the chance of a few boxes sitting in the manufacturer's back room. Those are issue's that will always be present in our hobby. Unfortunate...but true.

You asked: Would 'Destruction' of the chips, if some survive make them obsolete.."

If some didn't survive, they would be both obsolete AND extinct.