I'd really like to see the MOL HQ become a bustling beehive of activity over the next couple of years. Garth, Charlie, and the kid with the Golem would be good to have around. And they could introduce some new characters who don't die.
That's what I'm hoping they're building towards for the end of the series. The series can end with the deaths of Sam and Dean, but with a fully rebuilt Men of Letters. Throughout the entire series we've seen the horrible and lonely lives that hunters are forced to lead in order to protect the world, but the Winchesters' will leave behind a legacy of a better life for the next generation of hunters.
Of course, if they keep killing off people like Kevin and Tara that's not going to happen.