Great question, @lstepany
Our team has built a backup app for HubSpot (called Pro Backup) that backs up the relation between contacts, deals, etc. and their engagements. If you a contact, then the related engagements will be restored as well.
Or in your case: If you have deleted a number of contacts, then you would still be able to access the related engagements through the app.
Here’s a tutorial video that showcases the restore functionality for contacts: https://www.youtube.com/watch?v=YdGwplPajQ4
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