Do you have any sort of feel for if you will owe tax when you really file? For many people who are employees doing withholding, you are likely to get a refund. You can get a feel for this by running your tax return (but not filing!) with the code W amount one way or the other, just to see if you get a refund each time.
If so, then I would go ahead and file an extension. You won't owe anything in any case, so your position is OK. Then when you get your corrected W-2, you can file, knowing that you are doing it right the first time.
If you think you might owe some money when you finally file, then pay enough when filing the extension to make what you owe positive, then do the same thing: file when you have all the right forms.