DSLR and digital camera sales in general have gone down steadily for the last decade +
Recently, SONY took over the #2 spot, bumping Nikon down to 3rd.
Canon is no longer developing new EOS Lenses, instead concentrating on the new R mount of their new 'Mirrorless' system.
Nikon has made no such announcement, but does seem to be concentrating new lens development on THEIR new system.
It still seems possible that a couple of the smaller players, like Olympus, Panasonic and perhaps Fujifilm MAY consider merging. New camera development is costly and the competition is fierce. Each of these manufacturers does something better than others and the combination would be pretty good.