All the camera companies are facing major declines in volume. The market is declining by 18-20% annually. There is no compelling reason to buy a new camera today as there was 15 years ago. The cameras of today are excellent - but so are the 5 year old models they are replacing.
The low end of the market is infrequent consumer buyers. They get a lot better results with phone cameras than a full size camera, they don't post process or edit images, and most of the images have a final output on social media rather than a print. Prints are infrequent. That market includes the segment that will move up to enthusiast in the future, but it's mainly people who will put a camera in a closet and use their phone more and more. Nikon is decreasing emphasis on this market - and Canon has a similar strategy.
Nikon's mirrorless segment is actually growing - it's just falling short of overly aggressive projections. The cameras are good and the lenses are terrific. There are some niches where a DSLR is better - such as fast action - but for most use the mirrorless is better than their latest DSLR.
Nikon is facing writeoffs and restructuring as they shrink the business to match future volumes. You don't go from 20% declines to growth in a year or two. They are facing a 40-50% decline from today's volume before things stabilize. They are making a transition from DSLR to ML, but that's not going to be a big growth segment compared to the decline in DSLR sales. Why would a DSLR user continue to invest in lenses?
Canon faces almost exactly the same issues. They had a 17% decline in revenue, increasing inventories, and they lack any cameras compatible with CFExpress cards. They are fighting that with price by discounting older products. They have a growing mirrorless segment, but don't yet have the camera bodies to go with the pro lenses. Their strategy - like Nikon - is to target the enthusiast and professional markets. But they have reduced their sales and pro support staff, they provide less support to the Canon Explorers program, and they are struggling to maintain profitability. Canon indicated the transition will take at least two more years.
Sony has stopped breaking out all the detail for their imaging division - it's combined into a broader segment. They did a good job of moving to mirrorless - when their DSLR business was dying. They are well positioned but still are not seeing sales growth. When there is growth, it comes from discounting older models - which might be a good strategy. They do face issues with having a smaller mount, so the Canon and Nikon lenses will have a performance edge, and Sony will be in a position where many of their lenses are not as good as Canon and Nikon alternatives. Right now they have a good lineup - and performance is good compared to DSLR lenses - but Sony users will need to see an upgrade cycle to compete with the newer Canon and Nikon lenses (which benefit form the larger mount).
Nikon is in reasonable shape for now. You can go a long time making small profits - it's operating losses that kill you. Smaller competitors will exit first. Olympus is losing 30% of every sales dollar right now and has no real opportunity to increase sales. Fuji has a small niche market that is in decline. Panasonic is doing well, but it's in the small camera market and they face market declines. I'm not sure any camera company is "safe". Big companies that have money losing camera divisions are even more likely to bite the bullet and close money losing businesses.
Perhaps one of the most telling things about the camera market was the exit of Lexar from the market. The new Micron CEO - which owned Lexar - came from Sandisk. They looked at their businesses which were all growing rapidly, and decided the memory card business was better off discontinued since it was never going to grow or be worth investment of management time and capital. Micron could sell memory to others and not fool with the small Lexar product line - even with the number two market position.