My client's business is temporarily inactive. If he cancels his QB online account, can he re-subscribe within a year and still have access to the records as they are now?

You're right, usermalibumar2.
 

Your client can cancel their account for now, and renew once they're back on business. Make sure to remind them not to go over a year. The system automatically deletes a canceled account after a year of inactivity.

Their transactions and everything else will stay in one place. They can go back by the end of the year to file their taxes.

You can check this article for more information about the availability of their data: What happens to my QuickBooks Online data after I cancel?

Here's another one for future reference: How to resubscribe or reactivate QuickBooks Online.

Stay in touch with me if you have more questions.

Yes. But you should ask them to convert their data to QB Desktop file as for insurance.