Dear Theresa Calunsag,
Good day! Thank you for posting to Microsoft Community.
In order to understand your query and provide accurate information, May I please double confirm if users already have Exchange Online Plan 1 and Exchange Online Plan 2 has been assigned as an add-on plan? If so, when you remove the additional Exchange Online Plan 2, which will impact the archiving capabilities for tenant users. Exchange Online Plan 2 offers 100 GB of capacity and the ability to scale up to 1.5 TB using auto-expanding feature. Without this plan, users will revert to the limits of Exchange Online Plan 1, which includes a 50GB primary mailbox and a 50GB archive mailbox.
As a result, if a user has more than 50 GB of archive data in their archive mailbox, they will lose the items that stored above this storage limit. However, since you mention that, users have expanded their mailboxes but barely have any emails in their inboxes, so downgrading to Plan 1 can be a cost-effective solution while still providing enough storage space to meet their needs.
If you have any other question or I have got you wrong, please feel free to me know.
Thank you for your precious time. Have a nice day!
Sincerely
Libeamlak | Microsoft Community Moderator