In 99.9% of cases if you have rooted device you'll be able to receive information about OTA update but you won't be able to install it.
Same thing is for unlocked bootloader.
Root won't affect DRM keys but as we can't root Z2 (at the moment) without unlocking bootloader - your keys will be lost forever.
Right and proper way is to first root device, backup TA partition and then unlock bootloader...but, as I said, we can't root BL device for now...
You won't lose much if you lose DRM but I prefer to keep it.
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