When performing electronic discovery for web based email accounts, keep in mind that a outlook.com account may become disabled if a user has not logged in for more than 2 years. After this period, may not be possible to recover the data for the account at all. Outlook reserves the right to delete the data.
See the services agreement posted here.
OneDrive accounts will be closed after more than one year of inactivity. After a user voluntarily closes their email account, Microsoft will still permit it to be reactivated for another 60 days.