Everything that follows is personal opinion, so I can't provide an citations. Sorry.
Are they expecting us to all go back and live in caves?
Only a distinct minority. As with any movement, there is an extreme that recommends an extreme action. These people understand the physics and know there is no replacement for these power sources, but they don't care. Any cost is acceptable.
There is another group in the movement that I describe as the "corporate conspiracy" crowd. In my experience this group tends to blame corporate greed for the bad outcomes with regards to the environment. The topic of nuclear shutdown in Japan came up over a year ago, and I recall responding to someone that blamed greed for the location chosen for Fukushima. I pointed out that they needed a massive body of water to assist in cooling the plant and Japan isn't known for its huge rivers or lakes. They placed it somewhere with enough water to keep it functional, not because they were being overly greedy. I think the "corporate conspiracy" crowd only partially understands the physics behind power generation, and always assume corporate greed is preventing the better solutions from being available. To the extent that old reactors are still active, they may be right, but there really is no magical solution that will make everything better.
That leads me to the final group, the ones I feel have no real understanding of the physics behind power generation. My perspective on this group is that they become the proof of Arthur C. Clarke's Third Law. The technology is so hard for them to understand, that they treat it as magic. And of course, being magic, anything is magically possible. So obviously, solar and wind will work perfectly and everything will be great (magically).
Unfortunately, on the topic of nuclear power, those three environmentally focused groups are assisted by the NIMBYs and people with poor risk understanding. This group has no real interest in the environmental movement, but radiation is scary so we better not. It is like the risk problem we see with terrorism. Every once in a while something goes horribly wrong, and a small group of people is affected. Meanwhile, our usual day-to-day activities will cause more deaths every year than that occasional horrible event, but we will concentrate all our efforts in preventing that horrible event from ever happening again.
It really is a much larger problem than just the "environmentalists" described in the quote from your post. I don't know that I even have a solution.
