Wade Wilson is a man of many skills and abilities, but what's always been his most useful ability is Deadpool's healing factor. Much like that of Wolverine's (after all, both men were changed forever thanks to the Weapon X program), Deadpool's healing factor has allowed him to cheat death on more than one occasion. First by keeping his cancer at bay, then by allowing the anti-hero to withstand an onslaught of attacks that should have killed him.
From bullets to decapitation, Deadpool is able to regenerate any part of his body, healing any injury, as long as just one cell of his remains. For some, being graced with the gift of permanent life may be a blessing, but after a while, it's become a curse for Deadpool when Death comes for his daughter, Ellie. While Ellie's healing factor is better than Deadpool's, she still ages, unlike her father, meaning Wade is forced to confront the potential death of his daughter.
In Deadpool: The End by Joe Kelly and Mike Hawthorne, Ellie is 97-years old and is ready to die. Deadpool can't bring himself to go on living without her, but his daughter has a solution that allows them both to go gently into that good night together. She concocts a bevy of neutrino bombs tethered to a miniature black hole. The neutrinos exist to incinerate both of their brains before they even realize what happened. Then, the black hole quickly swallows the explosion left behind, destroying every single Deadpool atom before he could possibly regenerate. In short? Deadpool can finally die for good.
Countering a healing factor has proved difficult for any and every character in the Marvel universe, including Deadpool himself who struggled to kill the unkillable Madcap before settling on simply imprisoning him. Similarly, Deadpool's Weapon X comrade, Wolverine during his Old Man Logan days, struggled to end his own life, with his healing factor allowing him to regenerate after a head-on collision with a train. To Weapon X's credit, they built a superb healing factor gene that's virtually impossible to counter. While Deadpool's healing factor might be the opposite of Wolverine's, they both are powerful enough that it takes something incredibly powerful to get around it.
Until Deadpool: The End, a healing factor was always viewed by audiences as something that was completely impossible, but Ellie's successful scheme proves just how plausible it is to counter-attack. Even better, she's skilled enough as a hero of the future to find the perfect way to counter her father, Deadpool's, abilities. This comic goes to prove that even though Deadpool's healing factor is in many ways unparalleled and extremely difficult to defeat, it can still be overcome by one way or another.