Windows update just crashed my Outlook permanently.

Thank you, Windows Update.

All right, since this is a painfully obscure bug that stole 30 dev minutes from me, I'll share my findings here.

On Windows 10, in Outlook (2013 and perhaps others), if you go to the Add Signature screen and add a new Signature, Outlook will crash. Resetting whatever won't help.
In Event Viewer, under Windows Logs > Application, a recent Information entry with ID 1001 that says:

Problem signature:
P1: outlook.exe
..
P4: MSVCR100.dll

Fix (workaround):
> Go to registry:
HKEY_USERS\<YOUR USER PROFILE ID>\Software\Microsoft\Office\15.0\Outlook\Options\Calendar

To find your user profile id, run this in the Windows conmandline:

wmic useraccount where name='username' get sid
> username should be your username, e.g. john

Alter Calendar Type
> change the value of this key from 1 to 0.

Note:
This resets your favorites bar but that should be quickly resolved by adding your folders to your favorites bar manually again.

Courtesy of jaesson2 on Microsoft TechNet:
https://bit.ly/32niKPX