Is there a reliable autosave function for nodes?
Autosave


  The Autosave module automatically saves a snapshot of your content
  type form using AJAX. If the user's browser or machine dies while
  editing a node; the edits will be presented to the user the next time
  they return to the node. The user may toggle back and forth between
  the last saved version and the version with the edits that were lost
  and select which of these they would like to continue with.
  
  How often a form is autosaved as well as which content types to enable
  autosave for are admin configurable.