This is a legitimate concern about Google’s plan but I’m sure eDiscovery was the last of Google’s concerns about this:
“What will happen when program code is contained in email? How will lawyers establish that an email is the same as it was when written years ago when it ran an app or script that doesn’t exist anymore?”
This is actually similar to something like SnapChat or Instagream stories. If I know the material is going to disappear in 24 hours, the only way to prove it was there is to screenshot it. If an email is set to run a script once, or for a limited time, the same thing applies. I can’t “keep” the email if the content won’t be there anymore.
Screenshots, of course, are easily faked too. Courts, good luck figuring that one out!