I'd think so for all practical purposes. You'd need state of the art lab equipment to extract 2nd or 3rd layer raw encrypted data from the SSD and supercomputing decryption power to crack the AES 128 bit encryption.Thanks for the replies guys. For a home user, yes, you can hit the restore button and I'm sure you're okay. Business on the other hand....
Typically when I'm done with a PC I run DBAN and I'm done with it. DBAN won't run, and due to the UEFI requirement a lot of other utilities won't run as well.
Right now, the easiest solution appears to be: reset SP3 via restore partition --> encrypt with bitlocker (and wait for it to finish) --> restore again so it's clean when you turn it in. But does this make everything unrecoverable?
It also would seem likely the encryption keys are tossed when you reset. there's an option to do that in the TPM management console which makes all data unrecoverable to mere mortals. So the supercomputer decryption would have its work cut out for it. the estimate to do that is somewhere in the vicinity of half a million times the age of the universe but its likely to end before then.