For Movie Deadpool, I think it's fairly plausible that his powers would kick in if the collar stopped working fairly soon after clinical death, and maybe after electrical function ceased in his brain. I think once decomposition set in, taking the collar off wouldn't bring him back. The big metal guy, colossus, can easily yank the collar out of deadpool without hurting his neck.
Even if Colosus hurts deadpool's neck, so what? Deadpool will survive. Can Deadpool Die With The Collar On? Have you ever considered the implications of a mutant inhibitor collar on a character like Deadpool? In this engaging vi. Deadpool 2 gave us a taste of a potential fatal end for Wade, with the mutant inhibitor collars nullifying all powers, including Wade's ability to regenerate.
On Movies: New and Upcoming Releases, a GameFAQs message board topic titled "Can Deadpool die in the comics? (Deadpool 2 spoilers)". What does the collar do to Deadpool? But while Wade's healing factor could stop the disease from spreading, it doesn't cure him. During Deadpool 2, he's fitted with a collar that blocks his accelerated healing, causing him to become sick again after his tumors return.
For those wondering "Can Deadpool feel pain?" or "Can Deadpool die?", here is the need. Again: SPOILERS so if Deadpool died while wearing one of the icebox's power inhibiting collars, what would happen when the power cell finally died in the collar? Would his powers suddenly kick back in and revive him in the future (assuming there was something left of his body to revive)? The movie then fast-forwards through the rest of the battle, up to the point where Deadpool has put on the collar and Russell is about to kill the headmaster. Deadpool does his slow-mo dive again, Cable fires the gun, and Russell is once again stopped in his tracks by the realization that someone was willing to die to protect him.
Deadpool has a long history of cheating death, despite the fact that he's typically more than willing to die.