It can happen to anybody. Actually it will happen to anybody that uses WordPress long enough and has half a dozen plugins installed and a nice WP theme to drive his site.
Upgrades come on a daily basis and more often than not if your are administrator of the sie you will find the urge to Upgrade all just because it makes sense to have the last version of all your components that make your site.
And yes at some point it breaks and the only think that comes up is Internar server error 500. The less informative error of all. Just like saying,
“Something is up, can’t really tell you what.”
The worse thing that can happen is the WP panel is returning 500 too. Oh NO!! I cannot even access the tool that can help me fix what I broke.
Well this is why it is a good idea to have a Hosting Panel like Plesk or such.
I did break a WP site recently after a theme upgrade. Everything was returning a 500 error.
Plesk to the rescue
Plesk will give the basic functionality needed to sanitize your WP instance. In the worse case scenario you may need to deactivate all plugins and fallback to a basic default theme.
You can fiddle with the most basic configuration, like activate/deactivate plugins and themes until the page comes back to life.
Rollback to a working version
Rolling back manually can be a cumbersome task full o pits and falls. Although it is fairly easy when you have detected the component that failed, being a plugin or your theme, you can download the version before the break and install it like with the normal procedure.
WP Rollback will do that smoothly and in an easy-point-and-clicky way which can save a lot o time and pain.
Check it out in the WordPress official site.