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.
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.