According to the Google documentation on the limits of Adwords scripts:
OAuth2 is used to authorize scripts. Each account has a limit of 250 authorized scripts. Beyond that limit, one of the previously authorized scripts will be deauthorized. This is only temporary, and the script can be reauthorized the next time it is opened.
So, once the limit of 250 is reached, a random script from your account will be de-authorized.
NOTE: you don’t get any warning if your account reaches the maximum number of authorized scripts.
You can review permissions granted to your scripts and other applications by navigating to https://www.google.com/settings/security and clicking “Manage access”. From there you can de-authorize any scripts if you need to.
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