Hey Bill, these are my 2 cents as a newsletter agency owner- we send about 8 Million + newsletter emails per month so there's some data to back it up.
We ran a test where one of our clients ( roughly 10K subs) with 55% opens and 5.5% CTR in the business niche just went MIA due to a personal reason and after some buffer posts- we didn't have anything more to post at all.
So, for about 12 weeks we didnt post anything and this happened when we came back - the open rates dropped by about 12-15% even though the quality of posts were same/better. And the unsubscribe rate shot up.
I believe newsletters are extremely consistency based, so I would suggest building a buffer and automate that for the off season.
Hope that helps.