I highly doubt it will be canceled. First off, it's still one of the biggest shows on American TV. The Simpsons are very well-known, even if it isn't as popular now. It has the 'household name' status. That's enough to keep it going.
Secondly, really? They're not willing to take a (roughly) 50% pay cut on $8 million a season? Let's do some math for how much time they actually work:
20 minutes per episode (excluding intro, outro, and ad time. Also assuming all 20 minutes have some form of talking for each VA).
22 episodes in a season.
Let's be generous and say about 20 minutes of actually vocalization and getting ready per minute of episode time.
20 X 20 = 400 minutes
400/60 = 6.66 hours per episode
6.66 X 22 = 146.66 hours per season.
So for just under a full week of work, they get $8 million dollars. So they're going to quit if that gets bumped down to $4 million instead? Yes, I know they do have to do a lot of other things, but it's still a stupid amount of money overall.