The "chkAutosave" checkbox option (see [[AdvancedTiddlers]])
automatically writes the TW file to disk each time you press 'done'
from editing any individual tiddler. However, I think you are asking
for something that happens automatically on a periodic basis, rather
than in response to a specific user action.
I suppose we could set up a timer that periodically reads the
partially entered content in the input field, saves it to a special
'scratch' tiddler (e.g., [[AutoSaved]]), and then writes the TW file
to disk.
However, I'm not convinced that the extra protection this might offer
is really all that essential. Simply using the regular chkAutosave
option ensures that as soon as you press 'done', the file is
written... and even without autosave, there is a check before exiting
to warn you of any unsaved tiddler changes. You can also add this
plugin:
http://www.TiddlyTools.com/#ConfirmExitPlugin
which provides several extra 'safety' features to help avoid
accidentally discarding unsaved changes when exiting.
enjoy,
-e
Eric Shulman
TiddlyTools / ELS Design Studios