Deleted contacts will not change the open/click rates of campaigns. Their actions will still count toward the overall percentage for each report.
In the example below, there are 16 total Opens with 2 contacts. After deleting one of the contacts and refreshing the report, the 16 total Opens remains and the contact is gone:
Contacts that are deleted can still show in the specific reports (Clicks/Opens/etc.) but will not show on the Contacts overview page.
Below, the deleted contact no longer shows on the Contact overview: