Sure it does.. There is a reason WHY Spider-man and Batman have multiple forms of media, there is a reason why kids run around with Spidey sneeks and Batman undies, and not a Shazam T-shirt or Hawkeye hat...
Multiple media outlets lead to popularity which in turn can bring fans into the comic realm and increase reader numbers- thus making them more familiar, more popular and just the characters themselves but all characters associated with that world/book. There is a reason Spidey and Bats have been as popular and around as long as they have- outstanding rogues gallery only fuels that.
Because they were given a shot in the public consciousness and shown to garner interest in the mainstream. Shazam and Hawkeye have had basically no mainstream representation and weren't even given a shot really.
Yes, multiple media outlets lead to popularity and 85 percent of comics don't get multiple media outlets, just their comics. Given multiple chances of media doesn't automatically make your gallery better, just more well known.
Batman's Rouge Gallery is not outstanding, he has about 2 or 3 amazing villains, 4 or so good ones and the rest are meh or worse.
Edit: If Batman was given no other media beyond his comic ever would you say he still has one of the best Rogue Galleries?
The consequences of killing him vary depending on the story told. I guess a universal consequence would be Harley quinn going crazy and probably taking their men and gunning down random people. Joker is just crazy enough that he would have some stupid device on his heart or something. Once it stopped beating it would probably do something stupid.
I don't know...His character is setup in a way where no one EVER wants to have the Joker pissed at them...
This seems like a consequence that's worth it to put Joker down. Killing Lex RUINS Superman, not his character but "Superman" himself. Killing Joker ruins nothing.