Yes, there is a limit to the number of marketing contacts you can delete per organization in Zoho Marketing Automation. The limit is set at 100%.
This is to ensure that the users don't needlessly delete and re-add their marketing contacts repeatedly.
The limit is set at 100% for each organization based on the license purchased. If you have 1,000 marketing contacts, you can delete a maximum of 1,000 marketing contacts only. You can't delete marketing contacts for whom you've created campaigns; you've to delete the campaigns first before deleting them.