Hello @KWI Office 365 Admin
I guess you are talking about deleted user account feature in Entra ID. If that is the case, deleted users cannot be kept for more than 30 days as they will be permanently deleted after 30days. If you would like to keep this account for more than 30 days, I will suggest you restore the account before the 30 days and have the account disabled instead of deleting.
I hope this answers your question