No, they JUST extended him
Doesn't mean anything.
Coaches have gotten fired before their extension's even start.
AV was set to be in year one of his extension this year, but got fired at the end of last season. The Panthers extended Gerard Gallant 6 or 8 months before they fired him and I'm pretty sure that deal wasn't to start until 17-18, the year after they fired him.
I'm not saying he'll definitely be fired, but if he isn't, it won't be because he got extended. The only thing his extension means is that he's owed that money. They're not obligated to keep him for it, they're just obligated to pay him for it and with his reputation, he'll likely get a job immediately, as long as he's not fired during some bizarre time at the end of the summer. And then the team that hires him is on the hook for it.