There is probably a best-of-both-worlds solution of some kind, like, before the thing goes away a yellow div animation lingers up top stating "hover the mouse in the upper-right-hand corner of your browser window to restore the Seals-Nifty-Keen-Info-Bar", you know what I mean... and then, when it disappears, leaving a lingering 2-pixel div up there that allows one to get the bar back.  And then remembering how many times the user has seen that yellow bar in a cookie or database entry somewhere, and ceasing to nag them about it after the third time

But obv. that's a ridiculous shit-ton of javascript...  

Without the yellow bar stuff (I'm kidding about all that), leaving the two-pixels is sorta easy....  you'd still have some code to write -- you can't just instantly react to a mouse-over event by restoring the div, as this would make people go insane and have seizures and fold the nuts.  So you probably have to set a timer and poll for a couple of seconds, before you decide that they are legitimately trying to hover, and not just passing through on their way to the goatse.cx tab .

If you want it to look all fancified and beautimatized you could use jQuery easing for the transitions  .. you know what, I should just code this up and ship it to you.  Actually give me a 'lil bit and I'll do just that for you.  I'll see what I can't cobble together early this evening.

-w/e