Unless they get employed doing something else.
Suppose you have 10 people and 10 jobs. One job is eliminated by technology. Now you have 10 people and 9 jobs. That 1 newly unemployed dude tries to get another job, but to do so he'll have to oucompete 1 of the remaining 9 employed people out of their job. So how will he compete? Why, he'll do the job for less money. So now we have 9 people with lower average wage, and 1 unemployed dude. This merry-go-round will then continue. Also, as wages fall so will the total buying power of the workforce, which creates further downward pressure.
Capitalism cannot handle a situation where labour is not the resource that limits production. It predates Industrial Revolution, almost collapsed as a result of it, and is heading back towards the cliffs now that true believers have managed to convince themselves that the fall of Soviet Russia means revolution is no longer possible and dismantled the compensating systems.
The only real question at this point is whether it'll collapse into a dystopia where the poor are kept down by brute force, or incorporate sufficient income redistribution to guarantee a middle-class minimum income. US is trapped to the former fate by the aftereffects of Cold War rhetoric, but Europe and Japan have hope. And China, of course, is a dystopia as is.
"Remaining jobs" need not decline and it's worth noting that they actually aren't declining at present.
According to the article they do. Also, when was the last time job market was good for the employees?