- Yes. Once encrypted, always encrypted.
- Compliance doesn't make a distinction between the two.
- That depends on the process used. Per #1, the data will never be unencrypted unless the volume itself is unencrypted fully. Also, remember though that BitLocker is encryption of data at rest only. If a user can log into the device, then they can access all data on the volume encrypted using the current encryption keys. Thus, unless the volume has been wiped and the BitLocker encryption key has been rotated, the data will be accessible to the user. Simply reimaging doesn't do this.
For a complete A to Z on BitLocker plus Intune, see https://techcommunity.microsoft.com/t5/intune-customer-success/enabling-bitlocker-with-microsoft-endpoint-manager-microsoft/ba-p/2149784.