The University of Illinois ArcGIS online portal maintains active user accounts until the expiration of the member's NetID. (An active NetID is necessary to login to the online portal.) UI ESRI member accounts associated with an expired NetID (the member has left the university and is no longer an active student or staff member), will be removed from the portal. When an account is removed, the membership, entitlements, content and owned groups are permanently deleted. 

Graduated students and departed or retired faculty and staff should transfer their data from the U of I ArcGIS Enterprise portal prior to leaving the university. Any remaining content left behind shall be maintained at the discretion of the ESRI enterprise administrator. This may include actions such as transferring ownership of remaining user account assets to other requesting members or groups of the organization 

Related articles

• NetID Expiration Process for Each Campus
  https://answers.uillinois.edu/90853
• How to Transfer content to your next ArcGIS account
  https://community.esri.com/t5/arcgis-tutorials-documents/learn-arcgis-how-to-transfer-content-to-your-next/ta-p/909524
• U of I ArcGIS Online Feature Storage Limit 
  https://answers.uillinois.edu/137275