SpiderOak does not disable, freeze, block, or close accounts due to inactivity. So long as the account is in good standing, it will remain open.
Free trial accounts are canceled after 21 days if they were not previously upgraded. If you wish to keep your trial account, be sure to upgrade it before the 21 day trial ends.
If you no longer wish to keep your ONE account, you can cancel it by performing the steps listed here.