If you delete a class from you teacher account, there is no way to recover it unfortunately.
You can recover your students' data though.
To access your students data, you need to set up a brand new class and invite your students to the class again.
The data will then be visible in your 'Students' and 'Insights' tabs. You cannot recover completion data from individual assignments. However, the data for any work completed as part of an assignment can be found in the 'Insights' tab.