Flickr could have been Instagram and more if it hadn't been neglected for so long. I've renewed my Flickr Pro subscription for a year - it's an acceptable gamble at this point. I have no alternative for the service.
Except that's sort of my point. I don't much care about Instragram. I just accept that there's no unicorn photo service for people like me. If flickr goes down, I'd probably switch to Smugmug.
I don't know. Flickr is optimized around sharing photos (at full resolution if desired) to a broad audience. There is a largely optional community angle but a lot of us barely participate in that.
I have a short list of things that I wish flickr did better and there are doubtless things it could have evolved into without harming the store/display-photos use case. But, although it's been pretty stagnant I'm honestly not sure what more I really want it to do.
I agree it would be very unfortunate if flickr were to either shutdown or do something like turn off non-paid accounts. I find it a useful source of CC images and I am contacted from time to time by people wanting to use photos of mine.