Great question — answering as the UphillTech team:
A bit of a rushed answer since you're on the clock with the batter expiration. My best research at that, not being a food safety expert, indicates that you can keep it up to about a week, or until it smells off. At a glance, I'd guess that a half a cup of non-fat greek yogurt for two eggs is likely going to be far less fat, which will negatively affect your texture, but more importantly it's not going to produce the same sort of binding reaction that eggs would. Since you indicated you're willing to experiment, you could try adding the eggs alongside a bit of extra butter to fill in for the missing fat, then a dash of extra flour. If I had to guess at the quantities, I'd suggest maybe...
Full answer by Onyz: https://cooking.stackexchange.com/a/125222 (CC BY-SA 4.0).
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