It depends on how the plugin saves data. If it just processes the data (sending an email, for example), then the submitted data is lost.
If the plugin stores the data, it may be in the backup copies of your database, depending on when the backups were done relative to the form submittal. (You do have backup copies, right?)
The actual location of the data in the database (if that’s where it was stored) is in the source code of the plugin. It might be in the ‘options’ table, perhaps in a record at the ‘end’ of that table.
Or it may just be lost forever.