Your best option is to request the automatic extension of the deadline and file a joint return when you get the W-2 copy from his employer.
If you file separately, you will probably owe more tax or get a smaller refund than if you file jointly, and he will owe a penalty for filing late unless he files an extension request.
If you file a joint return now with one income and then amend later, you need to know that amended returns take 4-5 months to process. If the amended return results in a second refund, it will take that long to arrive. If the amended return results in a smaller overall refund (meaning you have to pay some of your refund back), you will owe interest and penalties on the due amount.