I talked to Apple Support and so far it is still not working. I was able to boot using the recovery partition "Disk Utility -> First Aid -> Repair Disk". When I ran Repair Disk there were some errors reported and repaired, then OSX still not booting.
After some research, I came across TestDisk. I attempted to repair the system, but after a few repair attempts the drive has now become read only and I can't figure out how to reverse that.
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Partition table type (auto): EFI GPT
Media is opened in read-only.
Disk /dev/rdisk2 - 500 GB / 465 GiB (RO)
Partition table type: EFI GPT
Analyse Disk /dev/rdisk2 - 500 GB / 465 GiB - 976773168 sectors (RO)
hdr_size=92
hdr_lba_self=976773167
hdr_lba_alt=1 (expected 1)
hdr_lba_start=34
hdr_lba_end=976773134
hdr_lba_table=976773135
hdr_entries=128
hdr_entsz=128
Bad GPT partition, invalid signature.
Trying alternate GPT
1 P EFI System 40 409639 409600 [EFI System Partition]
2 P Mac HFS 409640 975503591 975093952 [Untitled]
3 P Mac Boot 975503592 976773127 1269536 [Recovery HD]
Current partition structure:
Bad GPT partition, invalid signature.
Trying alternate GPT
1 P EFI System 40 409639 409600 [EFI System Partition]
2 P Mac HFS 409640 975503591 975093952 [Untitled]
3 P Mac Boot 975503592 976773127 1269536 [Recovery HD]