Janeway has to return. ...
I cannot understand why anyone would want her to stay dead.
That's because you're assuming it's personal. It's not. It's about wanting fiction in general to treat death honestly, to confront and acknowledge the loss. The death of a loved one is something we all have to deal with in real life, sooner or later. And fiction can help us cope with painful emotions like that. So it's not about hating a character or wanting them to be dead. It's about
facing the reality of losing someone you love, accepting and working through it, rather than trying to deny or avoid it. In real life, when a loved one dies, you don't get them back, but you don't stop loving them either. You cherish their memory and incorporate their legacy into your life going forward.
Which is exactly what Kirsten Beyer's VGR novels have done with Janeway. Her books have been pervaded with love and admiration for Janeway, even in the character's absence. Janeway looms larger over the books where she's dead than she did in many of the books where she was alive. So this has nothing to do with not loving Janeway.
No, she isn't. It's called
Star Trek: Voyager, not
Star Trek: Janeway. Like every other modern Trek series, it was created from the start as an ensemble show. It revolved around nine characters, not just one. Janeway had a larger number of focus episodes than any other single character, but she was the primary focus of no more than a third of the series' episodes. Just to be crystal-clear, that means that there were
twice as many episodes centering on other characters than episodes centering on Janeway. And in seasons 4-7, Janeway had only slightly more focus episodes than Seven of Nine did.
They
did kill off Kirk.
Star Trek continued.
Lots of people love Janeway. But many of us, hopefully most of us, are mature enough to realize that you can keep loving someone even after they die. In fact, we often get
more in touch with our love for people after they're gone.
Also, G already saved Picard once when he was hit with a plasma gun in the chest and his artificial heart stopped.
Assuming you mean Q, we don't actually know that. Picard was on the operating table in sickbay at the time. Q
claimed that Picard was dead and needed Q to save him, but Q is a notorious liar. We have no objective confirmation that Picard ever died on that table.
Stories suck when the main good guy is killed off. Look how the final Matrix movie TANKED after they killed of Neo and Trinity. You simply do not kill off the main chracter, even doubly so when that character is a good guy.
As with everything in fiction, there is no single universal rule that applies the same to everything. There are certainly series where the main character died and the series continued successfully thereafter -- including
Blake's 7, Robin of Sherwood, Earth: Final Conflict, and (this one's a few years old, but recent enough that I'll spoiler-code it)