If someone unsubscribes by clicking the unsubscribe link, they are not automatically added to the block list, their status changes to "unsubscribed" and the sequence stops for them.
There is no 'unsubscribe lead' button at your end hence you can manually delete the lead from your campaign.
If you change the lead status in Unibox or in the Campaign Leads tab to anything other than the default "Lead" status, the sequence for this lead stops. No more emails will be sent to this lead.
Then later on you can add that lead to the global blocklist, so that it does not get imported in the future in any of the campaigns.
You can delete a lead from your campaigns from Unibox, by clicking on a "Remove lead" button:
If you'd like to add this lead to a blocklist so you never upload it again to your campaign, check the box "Add to blocklist".
If you'd also like to remove other leads with the same domain, across all campaigns, check the box "Remove all leads from the same company".
If you'd like to learn how to delete leads in bulk, check this article.
⚠️ Important: Once deleted, data can't be recovered. All the data related to that lead will be deleted - unibox emails, campaign stats in analytics, etc.