You will be able to perform a bulk operation to reactivate the subscriptions on your Chargebee site. You will need to navigate to Settings > Import & Export Data > Choose a Bulk Operation in your Chargebee site and make use of the 'Reactivate Subscriptions' bulk operation to reactivate the subscription.
It is highly recommended that you try this on your Chargebee test site before performing the 'Reactivate Subscription' bulk operation on your Chargebee live site. Do click on the link mentioned below to view the documentation for bulk operations on Chargebee.