My guess is that Nikon is heading towards a niche market for quality digital cameras with sensible features and a more affordable line of smaller consumer oriented DSLR's just like they have now. The biggest problem they face is that the market for those products seems to be growing smaller and smaller.
When looking at the Amateur / Enthusiast market, I think that almost everyone who wants a DSLR probably already has one or more and the number of new customers keeps getting smaller as the number of gadgets available to occupy their time keeps increasing.
Impairments to a growing ILC / DSLR Amateur / Enthusiast market include
- The older gadget aficionados among us are losing our ability to cope with ever increasing complexity.
- Each new generation of DLSR and ILC cameras bring smaller and smaller improvements from the previous generation.
- The overwhelming number of things available to consume our free time
- Less free time available for the younger adult customers
- ... a number of other items that I cannot think of right now
How long Nikon will last is pretty much anyone's guess.
Canon has a broader market penetration with top end DSLR cameras and top end Video cameras. Sony has pushed in to the same space and of course there is the rest of the mirrorless manufacturers.
I am not sure what Nikon "should" do other than improve their customer relations (especially in the US) by providing first class service and clear support of their existing customer base much as the luxury car manufacturers do.