Compact flash definitely isn't going anywhere, it's the most widely used and supported memory format. That's not changing.

Which camera you should buy is going to be a balance of price and features. You should definitely check other cameras out but you need to balance having to buy new lenses when you already have some. I don't know if your lenses are any good or not. If they are then you might be reluctant to buy another brand, but you also need to check your lenses are compatible with the D50, not all nikon lenses work on all nikon SLRs.