John Mueller of Google said on Reddit the other day that generally speaking he has seen that it is faster for sites to return to the Google search results after experiencing site downtime than it takes for the pages to drop out of the Google search results.
John said “in the cases I’ve looked at, coming back after downtime tends to go faster than the dropping out because of downtime.”
Why is this, John said his “guess is (too lazy to check / ask) that we have some protections against dropping out of the index (slow crawl rate way down), and when things come back, we get excited and try to get that back as quickly as possible (increase crawl rate above normal).”
John also spent a lot of time replying how downtime impacts search results, saying it is not a “ranking” think.
Since this is done on a per-URL basis, and since we tend to recrawl important URLs (super simplified) more often, you’ll almost certainly see a visible drop in search traffic when we start dropping URLs. We recrawl most URLs somewhere in the range of hours to months, so you’ll generally see a noticable drop in indexing over the first week or so (your 5 days are right in there), with that tapering off for the next months (as we recrawl & drop the remaining pages). We’ll also slow down recrawling of URLs that we drop from indexing (but we don’t stop crawling them), so the overall crawl rate will drop too.
There’s no ranking change for any of this, but if your important pages drop out of the index, the remaining pages might not be that great for ranking, so it can look like a ranking change when you look at the site overall.
When things come back (assuming this is within the range of days to weeks, and not months after they drop), usually what happens is since we retry the important pages a bit more often, those will come back a bit faster. As they come back into the index, they’re usually back exactly how they were in the past, but it might be that it takes a bit of time for all of the signals to get reassociated with it, and depending on how much of the site got dropped, the internal linking etc also needs to be back first.
He shares a lot more detail in this thread, so it is probably worth checking out – although, most of you probably already understand most of this.
Forum discussion at Reddit.