Beginning March 26, 2018, once an AdWords account reaches 15 months without any spend, it will be canceled, Google announced this month. The reason is “to speed up the AdWords experience and help users stay within the manager account limits.”
After an account is canceled any unspent prepaid amount will be refunded back to the advertiser, and all ads in the account will stop automatically within 24 hours.
Google recommends that via the AdWords API, advertisers may want to run reports to gather historical stats for the date range where the account had activity before the account is canceled.
Advertisers will be able to reactivate the canceled accounts if the is under one or more manager accounts, and if doing so will not exceed the manager account limits.