Latest update to Sierra - iMac stuck at end of install

Hi,

I installed the latest update to Sierra about a week ago and let run its course. The install got stuck at the end of the status bar for more than a day.

I rebooted my iMac and it restarted the installed and went quickly to the same place and got stuck again. After 2 days, I rebooted again and the same happened.

I tried Cmd-L to get the log, nothing happens.

After reading a few posts on the internet, decided to reboot in safe mode (holding down the shift key after the tone and releasing it when Apple's logo appear).

Only when I'm doing this (safe mode), I'm getting a "Panic" display that only stays on for about 5 seconds. I was able to take a picture of it and it says:

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panic(cpu 2 caller 0xffffff800076f6cf): initproc exited -- exit reason namespace 6 subcode 0x5 description: Library not loaded: /usr/lib/system/libsystem_c.dylib

Referenced from: /usr/lib/libSystem.B.dylib

Reason: no suitable image found. Did find:

/usr/lib/system/libsystem_c.dylib: code signature invalid for '/usr/lib/system/libsystem_c.dylib'

Debugger called: <panic>

uuid info:

... bunch of hexadecimal codes ...

Thread 0 crashed

...

Mac OS version:

Not yet set

Kernel version:

Darwin Kernel Version 16.3.0: Thu Nov 17 20:23:58 PST 2016; root:xnu-3789.31.2~1/RELEASE_X86_64

Kernel UUID: 8DF81F81-019F-348E-B47E-40A448489E21

System model name: iMac12,2 (Mac-942859F58194171B)

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Now I'm stuck with an unusable iMac for about a week now.

I've seen somewhere that I can recover the OS but will that leave my apps and data intact or will I lose everything? Is that the only thing to do? I do have a backup but it dates back a couple of months... (I know, I should have done a backup before upgrading but I didn't...).

Thanks for your help!

Gim010