Workaround to bypass Salesforce SSO

One of the best practices for implementing Single Sign On for your Salesforce org is always ensure there is a way your System administrator can login via the standard login page side-stepping the SSO configuration.  Reason for this is if ever something goes wrong with your Idp provider's service and the SSO authentication responses are not coming as expected, all your users are unable to login.
That is, if you have setup your My domain to prevent logins via standard Salesforce login urls (login.salesforce.com). This includes the System administrator as well.

Only if your system administrator can somehow login, then he or she can disable the SSO settings for your domain and allow login via the normal login page as a temporary measure.

What do you do in such a situation?

Well Salesforce has built a workaround for this which is not well documented anywhere (probably for a good reason :) ). I found out about it from a colleague at work.
If your my domain url is - https://Companypersonal-dev-ed.my.salesforce.com , use the url -
https://Companypersonal-dev-ed.my.salesforce.com?login instead. It automatically takes you to the login page of your Org without redirecting to the SSO Idp provider. Thats it. So now you as the administrator know how to rescue your users when your SSO Idp provider plays the bad guy.

Enjoy!