I wouldn't exactly put it that way. It takes no courage to bring a major comic book character back from the dead, given how many times it happens. It does take some editorial courage to keep them dead, because it happens so less often. They still want to tell stories about the character every so often, but all of them seem to at least partially narratively rely on the fact that he is dead in a permanent kind of way rare to comic book characters.
Captain Marvel's death is interesting because unusually the story of his death is not the story just of his body ceasing to live, but about how his spirit itself moves on. That he transcended his physical death is now considered the defining element of his character. That's why bringing him back permanently is in some respects impossible. Not because its impossible to pen the words, but because any Captain Marvel that came back permanently wouldn't be the same Captain Marvel because of that fact. It would be like making a Batman whose parents lived: its not impossible to write the story, but it wouldn't and couldn't be the same Batman.
When THANOS was restored in the Silver Surfers by Death herself, he had learned and grown from his experiences both in life and in death and was more knowledgeable and wiser about some things. He was still Death's agent and had the whole nihilisitic phase to grow out of, but even without that now he is still Thanos.
Mar-Vell could also be more mature and wiser about things if he were brought back, plus he is still cosmically aware, which is ironic given that power gives him access to all knowledge about things and he couldn't divine a cure for himself.
Also I do remember in the past some editors and writers expressing a reluctance to bring him back due to how he died. Also some fans in the past have expressed their opinion that it would be a slap in the face to all cancer victims and their families if he were brought back. Personally I think that is taking things a bit too far, but that's just me.
I've read many cosmic stories from Marvel before and after Marv was killed off. With most of them I can honestly say that they would be better if Marv was there. Infinity War and Crusade being two good examples.
Sure the other cosmic heroes have stepped up a bit, including Richard Ryder Nova, but that doesn't mean much when the character is suddenly bumped aside and replaced with some stupid kid character just because Jeph Loebs son was a fan of Nova. Hello Marvel, remember there was a Nova Corps? As in more then ONE Nova??? Not that hard to have both of them is it?
As to Carol Danvers as Captain Marvel, I don't mind that she has the name as it is fitting she use it since she got her powers when Mar_Vell saved her from an explosion. Too bad the stories of her current series aren't that great. Also they could revive MArv, have him live with his girlfriend and raise a family and have him show up from time to time and still keep Carol as Captain Marvel. It's not that hard.
However with Secret War coming and the rumored massive reboot of the MU as a result, we shall see what happens. The picture of the cover of the first issue does show someone in a green and white Kree Captain military uniform flying around...perhaps an earlier version of Mar-Vell?
Marvel Comics has the trademark to publish a Captain Marvel book and for years they have kept it with one shots, mini series, regular series, etc. Too bad they can't work a deal with DC to obtain the rights to the original Captain Marvel or SHAZAM as he is now referred to. DC can use SHAZAM but they cant publish a book titled Captain Marvel, they screwed up and let that trademark lapse and Marvel snatched up and created Mar-Vell