Futurama has been brought back, but is now airing on Comedy Central...
As for the Simpsons, it has one good episode every season after number 10, which is very, very poor. It should seek to make every episode enjoyable, rather than just put out a load of same-y blandness and the one good episode. I litreally cringe watching any new episode that airs now.
I've never watched any of the other shows you mentioned (except Futurama), but on the point of Family Guy which other people have brought up, that's gone down the toilet to. Apart from Road to the Multiverse, Brian & Stewie and a couple of others (plus the Star Wars spoofs) any recent episode is just boring. I think, like Matt Groening moved everything decent to Futurama, Seth McFalane moved every decent into American Dad! which is much funnier and deserves more credit than is given to it.
Back to the Simpsons, i think, due to Fox's terrible management, if they did cancel Simpsons, they'd have nothing to go on within a year, and would therefore crumble. It would be like Nintendo giving up on Zelda and Mario, or Sega giving up on Sonic. They're all due for retirement, but their creators litreally can't let them go.