You misunderstand, the tragedy doesn't actualize because the tragedy is recognized before it becomes irreversible. The commons being grazed on were never depleted. The hypothesis is that it would be after several real life examples have proven the scenario false, we need to recognize the Tragedy of the Commons as a fallacy.

The real life scenarios have all been resolved through shared, communal decision that had specific frameworks for sharing as well as a progressive punishment structure for bad behavior. Ultimately there was never a tragedy and only an oversimplified thought experiment would result in the original outcome of totally depleted resources.