One of the single most important additions to the Super-Mythos happened when "Superman" wasn't around.
Bud Collyer, voice of Superman on radio and Filmation cartoon series (and first host of classic game Show Beat the Clock), was taking time off from the show. Rather than recast the role temporarily, the writers came up with Kryptonite, a metal from his home planet that weakened him. They locked Superman in a closet with a box of the stuff, and all the replacement actor had to do was moan a little. When Bud got back, they solved the deathtrap and went on with the show. Super-fans are happy to relate that a great deal of the most important parts of Superman today came from the radio show, including the aforementioned debilatory mineral, Jimmy Olsen and Perry White, and his ability to fly itself (not to mention the catchphrase "Up Up and Away")
The last time Superman died (there's a statement you don't get to use too often, outside of comics and Church) they spent several months without him in the books. To fill the void, they created four brand new characters to attempt to fill the void left by the big man: John Henry Irons, AKA Steel, the humanoid form of The Eradicator, the character known as the Cyborg Superman, and the new Superboy, eventually known as Conner Kent.
People commented that it was insane to take the character out of the books that bore his name, that it was pointless to do since it was only a temporary sales gimmick, etc etc etc...
Can you see where I'm going here?
Out of those four characters, two are still in active use, one is rumored (OK, I guess when they show you the character in a "Coming Soon" tease, it's not a rumor anymore) for a return BUT quick, and there's a general feeling the fourth may re-appear during the World of Krypton arc. In short, they ended up with four very strong characters that got used for over fifteen years now. Not bad for a gimmick.
They're not killing Superman this time, but as I've gone on about before, he's moving to New Krypton for about a year of "Real World" time (no idea how long DCU time, but I'm betting the whole story will be about six-twelve weeks all told). And once again, people will be trying to span the gap.
Some of the best moments in television history happened when the main character of the show was away and the supporting characters stepped up and became more three-dimensional characters.
Of course, you also can end up with the last seasons of Happy Days and Welcome Back Kotter. But there's a very important difference. Ted McGinley does not work for DC Comics.