I found a partial answer to this. If you use Goodnews or another method of creating subscribers (and thus MODX users by default), if the user doesn’t get assigned to a Access group (for example Members), then if they unsubscribe, they will be deleted from MODX entirely. However, if the user is part of a access level group, then if they unsubscribe, their user account will still show up in both the MODX user table and also the list of Goodnews subscriber emails (although they won’t be part of any mailing group any longer) and not be deleted.
In Goodnews, you can filter the list of subscribers that are not currently assigned to any Goodnews Group (thus they are not subscribed) through their default subscribers view. However, this list is slightly deceiving as it includes emails that are not currently subscribed to any mailing list (but didn’t explicitly unsubscribe) and also emails that explicitly unsubscribed so there is no way of actually differentiating the two when you view them in the backend.
For my purposes, this might be ok since I think we can treat the two groups as the same, but it would be nice if Goodnews had a option to view explicit unsubscribes.
@vibedesign, thanks for your input. I agree I would like my info treated similarly, but the reason I thought it would be important to keep the list is to ensure that explicit unsubscribe emails don’t get accidentally added back again. I agree, I will likely export list prior to importing to maintain the integrity of the list.