Did your pc literally catch on fire? Even the most dustiest pc's don't often ignite. You need a spark...
I'm suspecting a figure of speech, as we are talking about someone playing w3.. and its likely the components in any pc attempting to try this seriously would be new enough not to ignite. Still, id love to see a picture (or screenshot) if it did happen.
I still out of nervousness back up my saves every patch, more for the ini file changes it used to cause, but without cloud saves just make a 7zip and stick it in dropbox. Dropbox is awesome to use as your junk you'll never use again but still don't want to delete folder. Savegames yeap.