My understanding is that should not means that you should not try to retry. If I do retry than the other party can rightfully claim that I am DDOSing their service, trying to send emails to deleted accounts or put me on a spam list. I do not think that ignoring the RFC and trying to cover up for Google is the best course of action here. Maybe, just maybe, this is the right time when people realise what does it really mean to have an entity like Google. Because as it is stands, we are going to have the DNS infrastructure moved over to them with DoH and a similar outage is going to be even more devastating. The internet was designed to be resilient to failure because of its distributed nature and right now it just shows why concentrating resources in one place is bad.
You "should not" repeat delivery in basically the same way the mailman "should not" knock a second time if he's told the recipient doesn't reside at the designated address. What "should not" means in these cases is: "knock only once, and assume you're being told the truth in the absence of further evidence to the contrary". But when you clearly saw the recipient reside there yesterday, it makes sense to try to knock and catch him again tomorrow. Because, you know, maybe something went wrong, e.g. maybe the person who opened the door didn't recognize the name (or whatever). At the end of the day, the mailman's job is to deliver the mail with minimal disruption, not to play hot potato with envelopes.
The terminology is well defined [0], so in this case, retrying is not ignoring the RFC.
It's a difficult one though, because as you rightfully state, covering up for Google is not the best course of action for the system as a whole, yet it's likely a good course of action for those users who didn't get their emails.
[0]: 4. SHOULD NOT This phrase, or the phrase "NOT RECOMMENDED" mean that
there may exist valid reasons in particular circumstances when the
particular behavior is acceptable or even useful, but the full
implications should be understood and the case carefully weighed
before implementing any behavior described with this label.
