When you delete a data point in Mango the history will be deleted on the next nightly purge so it's important to resolve the situation before that happens.
I'll assume you are using the H2 data for your configuration and the NoSQL for the history. On the system setting page you should see the option to restore the H2 database from a backup. Click the "Get Backups" button to load in a list of available backups. Select the one you want and then click the Restore database button. If the database you restore has the deleted data point in it then all should be back to normal and your data should still be available for the data point.
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