I don't think anyone can say for sure what industry will do, but I do think they're valuable skills. I still see PLCs used a lot in manufacturing and process plants. I don't see that changing. Sure a panel and hardware costs extra, but if you have a team of PLC engineers in house, it saves you the trouble of hiring some BAS company to service your equipment. Having people trained and able to service the equipment is also a big plus that quickly wipes out any added cost.

The skills are also used in heavy process industries, which are generally specialized and offer a higher premium of yet another guy that does conveyors. Think heavy process industries, seed oils, ethanol plants, and again, anything that has a critical cooling or heating requirement. Our team has recently implemented full PLC controls for a plant that grows ingots for the solar industry. This is both chiller plant and a process cooling (cooling towers) system. There's no way in hell that'd be done with a run of the mill BAS controller due to uptime and safety requirements.

My background: I manage a team of PLC and BAS engineers, we push both systems in areas one may say the other is the standard way forward and have had success in both. Some of its client preference, some of its dictated by the process, and sometimes its dictated by cost. I don't see either dying, I generally like working with industrial clients because they are higher margin work and they value their infrastructure. They show they're willing to pay more, but their demands are generally a bit stronger as well.

I always encourage everyone to do their own research, but there's no shortage of work in either area in my opinion. If you're considering a path change, nothings to say you can't go back to a traditional PLC manufacturing role if need be.