Asgard is dying off because we don't have the time to really devote to it, and the folks who have been doing layout and editing would rather be devoting their time to something that might see actual print. All the writers who submitted articles that weren't used are free to have them back for their own purposes, and if you've lost an article that you submitted, email me with the details of what it was (it's hard to keep track of names, screen names, and articles, and who's who where), and I can send it back to you.
No online magazine that I know of is exactly taking Asgard's place. Instead, most of the effort we were spending on Asgard will instead be turned toward the ENWorld Player's Journal, the first issue of which will be coming to stores later this month.
I'm not entirely pleased that we're ending Asgard, but it was a lot of work, and it was taking away from time we could be spending on more fully developed books.