Personally, I would file the extension, in case there is a surprise on the Corrected W-2.
Since you have already done the first pass and seen that you will get a refund anyway, that simplifies your 4868 (the form to request an automatic extension).
File your extension (which gives you until October to file), and when your Corrected W-2 comes in, file when you add it to your return, even if it happens to be before April 18. But with the extension, you are protected from surprises.
