For us, live? Not much -- probably just whatever it is that YouTube provides for. At a glance, that's officially 40Mbps or less. (My anecdotal experience suggests that it is much, much less.)

But NASA's own in-house stream probably won't consist of 260 Mbps of video, either. Keeping headroom available during streams is important on packet-switched networks, which I [perhaps erroneously] assume this is.

(Later on, after the fact? That's what FOIA requests are for if you want to see every recorded bit. It will certainly come at a price, but if a person wants to compare the received friggin-laser-beams stream to that which the on-board video systems recorded internally, then it should be possible.)

Hopefully something nice. I don't think I've ever seen a 4k bluray but fine detail such as stars and dirt tend to get disturbed in compression pretty quickly.