Feel worried. Well, well-indexed pages got their URLs changed in Google to HTTPS which is making the pages go to 404. Have a plan. Need advice.
Spend the next week moving content over to HTTPS. Do nothing else.
Or, add a <link> element with the attribute rel="canonical" to the <head> section of these pages: <link rel="canonical"... And, wait for re-indexing?
Or, do both?
Or, move ONLY the incorrectly renamed (http --> https), but still highly indexed, pages to https. Then, just add the canonical link to all the ones that are still correctly listed.
My thinking here is: if Google went ahead and switched some pages to https on their own, and we've GOT https, just move as many of them over as we can?
Or, is it a better use of time and staff to fix only the ones we can see that have been switched in Google, and then put the "canonical" on the ones that are still shown correctly in Google as http? Will that "canonical" tag keep the pages from being reindexed? Or, is this more of the move to all as https, and inevitable - we should just make them all go to https?