If you have stored all your drawings in your iCloud Drive, they will be safe should you lose your device or delete Concepts. When deleting the app, iOS will inform you that the data stored in iCloud Drive will not be deleted.

If your drawings are stored locally (under On This iPad in the Gallery), they will be lost if the device is lost or Concepts is deleted from your device. They can still be recovered if you have enabled iCloud backup on your device and have a recent backup available from before the app was deleted.