Yes, a change in layout can affect site visitor behavior in many ways.

Some revamps actually do increase activity. I'd give it six months to gather enough data to make the decision.

In the early AdSense days, I experimented quite a bit with different ad sizes, colors and placement. After many months I found what I thought was the best possible combination and so I just left my site like that. Recently my thinking began to change about how I had things set up and so a new layout was in order. So far so good. Not amazing results, but at least not any worse than before.

User behavior changes over time, and a site layout which works perfect with AdSense on a given moment may give bad results a few years later. I experienced this with the vertical AdLinks unit which I added to a specific location on my site just after AdLinks were introduced. The link unit was the best performing ad unit of the whole site according to my channel statistics, but after some years the income from the unit fell down drastically. Recent experiments with layout and ad positions showed that visitors were using the site in a different way than previously and a rearrangement of the page elements was necessary to get the ads on a position again where the visitor would see them, and would be willing to click.