We don't optimize for well-being, we optimize for what we (think we) want, which are two very different things.

Natural selection does not cease operation. Say, for example, that someone invents a box that fully reproduces in every respect the subjective experience of eating and of having eaten by directly stimulating the brain. Dieters would love this device. Here's a device that implements in extreme form the very danger that you fear. In this case, the specific danger is that you will stop eating and die.

So the question is, will the device wipe out the human race? Almost certainly it will not wipe out the entire human race, simply because there are enough people around who would nevertheless choose to eat despite the availability of the device, possibly because they make a conscious decision to do so. These people will be the survivors, and they will reproduce, and their children will have both their values (transmitted culturally) and their genes, and so will probably be particularly resistant to the device.

That's an extreme case. In the actual case, there are doubtless many people who are not adapting well to technological change. They will tend to die out disproportionately, will tend to reproduce disproportionately less.

We have a model of this future in today's addictive drugs. Some people are more resistant to the lure of addictive drugs than others. Some people's lives are destroyed as they pursue the unnatural bliss of drugs, but many people manage to avoid their fate.

Many people have so far managed the trick of pursuing super stimuli without destroying their lives in the process.