If the card is defective and you can't access the data from it, then there is no way to get said data. Once a card is converted to "Internal" storage it is encoded and only to that one device. So no other devices can access the data and the data can't be ready any other way.
Additionally, if the phone was ever reset, then you would also lose access to the data on the SD card. The only way data on a card isn't encoded is to have left it as "External" storage.
To keep data, files, photos, etc., on a card you don't need to convert it. That only needs to be done if you want to keep apps on the card. Which, if installed directly to the card after it was converted to "Internal" storage would not be movable to the phone. Only apps that were first on the device and then moved to the card are able to move back to the device.
As stated originally, if the card is defective you likely won't be able to get any data from it. The only thing I can think of that you 'might' be able to try is to connect the phone to a computer, with the card still in the phone, and see if the computer can read and access the files. Again not apps. If the computer can access them, then you can move the files over to an empty folder on the computer and then when you remove the SD card you can move the files back to the phone itself (or wait until you get a new SD card). Other than that, there would be no way.