Well, yes and no. Sure, you can get hit with an algorithm change or penalty that destroys all your traffic. However, if you have good people who know what they are doing, this is not likely to happen, and if it does, it is easy (in most cases) to get your visits back. Panda and Penguin are another story, but if you get hit by those it is typically not accidental.
Another good thing to look at is domain authority and core page authority. If your site has had a few redesigns, moved URLs, or anything like that, it’s important to make sure that the domain authority has carried over. It’s also important to look at the page authorities of your core pages. If these are much lower than when they were before the organic traffic slide, there’s a good chance your redirects weren’t done properly, and the page authority isn’t being carried over through those new domains.
Google measures average time on site by first collecting each visitor’s exact time on a particular page. Imagine that a visitor lands on page 1 of your site. Google places a cookie, including a unique code for the visitor and a time stamp. When that visitor clicks through to page 2 of your site, Google again notes the time, and then subtracts the time that the visitor arrived at page 2 from the time that the visitor arrived at page 1. Google then averages each and every page’s time spent to get the average time each visitor spends on the site.
The amount of dark social that comprises one's direct traffic is going to vary. For example, you might be diligent about incorporating tracking tokens into your email marketing campaigns, and asking your co-marketing partners to do the same when they promote your site content. Great. You won't have a huge chunk of traffic dumped into direct traffic that should really go into email campaigns. On the other hand, perhaps you're embroiled in a viral video firestorm, and a video on your site gets forwarded around to thousands of inboxes ... you don't exactly have control over that kind of exposure, and as a result you'll be seeing a lot of traffic without referral data in the URL that, consequently, gets bucketed under direct traffic. See what I mean? It depends.
Love the five different area of investigation that you went over, great way to analyze and diagnosis the issue. I would also definitely agree doing a rankings comparison between the two time frames, and not only check what your Google ranking is, but also track the search volume for your keywords to see if it has fluctuated or gone down. Google Trends is a great tool for this as well, as one of your keywords that your ranking for may have just lost popularity online.
There are a few key pieces of information that we want to look at with Organic Traffic. The first piece of information that helps us frame the website performance is the total percentage of traffic that is organic traffic. These numbers will vary greatly based on your AdWords spend, how many email campaigns you send and many other factors. To view this figure, we want to go to the Acquisition section of your Analytics dashboard and then proceed to Channels.
Beyond organic and direct traffic, you must understand the difference between all of your traffic sources and how traffic is classified. Most web analytics platforms, like Google Analytics, utilize an algorithm and flow chart based on the referring website or parameters set within the URL that determine the source of traffic. Here is a breakdown of all sources: