OS Sierra installation failed - can't see HD in Disk Utility
Attempted to install OS Sierra, installation hung at grey screen. Rebooted to kernel panic and boot loop eventually ending with ø (Circle with line through). Won't boot into safe mode. Can boot into recovery mode, but can't see anything other than the recovery partition in disk utility. Made a USB bootable installer, booted from that, but again, could only see the recovery partition. Can't use backup or install sierra again because there is nowhere to install it. Tried in terminal: diskutil unmountdisk was successful, but diskutil mountdisk came back "One or volume (s) failed to mount"
Took the computer in to a service centre locally for diagnostic and tech said the SSD has failed. Does this sound like a reasonable diagnosis? Just wanted to check here before shelling out close to half the value of the laptop new for a replacement SSD.