weirdly enough, the ending is far less bleak than Empire's.
This film ends on an upwards trajectory, it ends rather hopeful. Sure, not everyone (sadly, that includes all the characters we've grown to like throughout the movie) made it out alive, but, to me, it's far less bleak than having Han frozen and abducted, Luke rather depressed, and the Empire strong as ever.
I felt it was a majority of ships. (that hadn't been blown up in the battle before)
The fact that Vader simply physically blocked that one Cruiser from jumping with his own ship, was super cool.
As soon as they set off as 'Rogue One', i'm quite sure that everyone knew this was to be a one-way trip. It's what makes their sacrifice even more meaningful. I think it really helps Cassian as a character, too - He was willing to sacrifice many lives for the good of the Rebellion (see his introductory scene), seeing him knowingly sacrifice his own life was the kind of redemption he needed.
Now that i had a good night of sleep - it's rather weird that Leia / Captain Antilles bother to go all "this is a consular ship" - "we're on a diplomatic mission" in ANH, when they pretty much know that Vader pretty much took down their license plate number when leaving the scene of 'death star plan theft'.