It will be incorrect when you file it and then you will have to amend when you dig up the missing W-2. Or you can ask for an extension and file later when you get it. But an extension does not give you extra time to pay tax you owe. If you expect to owe tax you need to pay your estimated tax due with your extension request.
If you are getting a refund there is no penalty for missing the deadline.
https://ttlc.intuit.com/community/tax-topics/help/how-do-i-file-a-tax-extension/00/1005116
W-2's come from your employer, and they have until February 1 to issue it. Some employers allow you to import the W-2 through the software, but for security reasons you still need information from the actual W-2 to import it. You might need to phone, drop in, email and/or snail mail an old employer to make sure they know where to send your W-2.
https://ttlc.intuit.com/questions/2561916-how-can-i-get-a-copy-of-my-w-2
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
