Use case is to update the subscriber status from SFMC to Sales Cloud.
Did you check the documentation for Marketing Cloud Connect?
There are multiple ways to unsubscribe a subscriber from receiving communications.
- A subscriber opts out by clicking the link to the profile center included in each email. The user is unsubscribed in the Marketing Cloud and the Email Opt Out flag is checked in the CRM.
- A subscriber can click a link to a custom profile center and opt in or out of specific communications.
- A Salesforce user can unsubscribe or opt out a subscriber manually within the CRM.
- A Marketing Cloud user can unsubscribe or opt out a subscriber manually in Marketing Cloud.
The first point above tells you, that using the connector and standard preference center in Marketing Cloud, while relying on Email Opt Out field on your leads and contacts, this should be a straightforward case to solve (if it isn't already so, without you knowing).
Basically it all comes down to, how you define your consent data model in Sales Cloud, and whether you use standard subscription center in Marketing Cloud. Then you of course also need to use the Contact/Lead ID as Subscriber Key in Marketing Cloud.