O365 Exchange Online litigation hold behaviour for deleted mailboxes with a fixed hold duration

Hello

We are using O365 in a hybrid configuration, and I refer to mailboxes for sync'd users.

I want to apply litigation hold to mailboxes with a duration of 366 days.

I understand that permanently deleted mail items (by user or retention policy) are reserved as purged items for the duration of the hold from the mail items creation/received date.

Questions I can't seem to find the answer for:

1. What happens to the regular non-deleted mailbox items once the associated Azure AD user is de-sync'd? Are they purged using the hold date?

I have yet to find an article that explains this… if anyone can enlighten me I’d be very grateful.

Cheers

Dan