Warning: spoilers ahead for Episode 14 of Agents of S.H.I.E.L.D. Season 5, called "Principia." If you haven't caught the episode yet, you may want to check out some of our spoiler-free articles until you get the chance to watch.
Agents of S.H.I.E.L.D. delivered a shocker at the end of the arc that took the characters to outer space (and the future) with the reveal that Phil Coulson is dying, and the 100th episode explained exactly why he's circling the drain. When Coulson was possessed by Ghost Rider at the end of Season 4, the Spirit of Vengeance exhausted the supply of Kree science in Coulson's body that had led to his reanimation with the T.A.H.I.T.I. project, and he's wasting away. That said, it's difficult to imagine S.H.I.E.L.D. killing off its lead character (and connection to the larger MCU), and "Principia" may have just established how the agents will go about saving his life.
The return of Mike to lend a hand (and attend a wedding) in the 100th episode was apparently more significant than just bringing a character back from the pilot to celebrate a milestone. His reappearance reminded the agents (and the audience) about Project Deathlok, which turned Mike into a cyborg against his will. The project was created way back in 1990, and the experimentation led to John Garrett becoming the first ever Deathlok soldier. He also ultimately became a supervillain who did a lot of damage to innocent lives and S.H.I.E.L.D., and he was the big bad of Season 1. His significance in Season 5 has everything to do with how he was able to live as long as he did.
In "Principia," the agents realized that Project Deathlok could be the way to save Coulson's life. While trying to track down gravitonium, they came across some folks familiar with Project Deathlok and the processes that saved the life of John Garrett and allowed Mike Peterson to survive. Coulson immediately shot down the idea of Deathlok tech extending his life, explicitly mentioning Garrett and declaring that he didn't want to follow in Garrett's footsteps. Daisy and May weren't so easily dissuaded, however, and they decided to continue pursuing a way to save Coulson's life via Deathlok tech.
On the one hand, Coulson deserves to have his wishes respected, and he decided that he's had enough of sketchy tech prolonging his life. On the other hand, it would be a bit rich of him to flip out at Daisy and May for taking actions against his will to save him. Admittedly, he might have a point about May, but Coulson literally shot Daisy with an ICER and dragged her back to Earth from the future despite her determination to stay at the Lighthouse and prevent herself from ever destroying the Earth in the past. If Coulson was allowed to save Daisy whether she liked it or not, I'd say Daisy deserves the same chance.
Of course, if they do find a way to use Deathlok tech on Coulson, they'll still probably need him to cooperate. On top of that, Coulson's flesh is actively necrotizing, and the agents may need to move quickly if they want to save much of Coulson's body. He may be fine with having the fancy prosthetic arm, but something tells me he's vehemently against going full cyborg like Mike. That said, perhaps seeing Yo-Yo adjust to having two of her limbs replaced with technology will get Coulson to realize that there are worse things in the world than relying on technology to stay up and about.
We'll have to wait and see. New episodes of Agents of S.H.I.E.L.D. air on Fridays at 9 p.m. ET on ABC. For more viewing options, be sure to take a look at our midseason TV premiere guide and our 2018 Netflix premiere guide. For the shows that need to be saved from cancellation (including S.H.I.E.L.D.), check out our list of the most likely candidates.