Chumbucket will die, causing Max to go on a Roaring Rampage of Revenge.
While at first Max will be using him simply to get payback for the theft of his car, He'll eventually get attached to him. Max has been in The Wasteland for so long, he'd be desperate for companionship (It's human nature.) Eventually, Scrotus and/or his warboys will kill him, Causing Max to go mad- Subverted: it's Hope and Glory who get killed off, although it does lead to Max taking one HELL of a Roaring Rampage of Revenge. Chumbucket also dies when Max rams the Magnum Opus into the Land Mover.
This version of Max was a child when humanity fell
He and Hope appear to be around the same age, and her bio states that she was born in the early days of the apocalypse. If Max had a wife and child before the fall of humanity, than that would mean he's old enough to be her father. You could argue that Max is Older Than He Looks, but I doubt that he would look so youthful in his old age, due to the fact that he seems to eat nothing but maggots, dog food, and lizards. I think it's more likely that he was a child when the world ended, and that the two people in the first history relic (whom explicitly refer to Max) is his mother and sister. Max has some kind of prejudice against Russians.
In Fury Road the Buzzard gang are seemingly normal Russian guys in gas masks but in the game they're weird monsters who make animal noises and have guzzoline for blood. This could be because we're seeing them from Max's perspective. He might blame the Russians for the apocalypse, considering a lot of the nukes that went off were probably theirs and they may have fought Australia directly in the Oil and Water Wars. Also since Max has a Polish-sounding surname and the two cultures have rarely gotten along. Griffa is Max's subconscious
Obviously, there's the fact that no one other than Max sees the guy. Further, some of Chum's lines when stopping for a level up indicate that Max is wandering off to stare into space for a while. So he's not physically there, but what is he? All of the conversations with Griffa involve him trying to force Max to remember his past or acknowledge the consequences of his actions in the present, eventually pointing out that Max is making friends (with the stronghold leaders, mainly) in spite of his best efforts. Max, in turn, increasingly desperately tried to shut Griffa down, insisting that he's just surviving in order to remain in his semi-feral autopiloted state. This implies, then, that Griffa represents the repressed civilized part of Max jostling loose and attempting to reassert itself. Max can't handle this, whether because he's too afraid of losing his life again, he's too comfortable in his survivor rut, he's completely lost it, or some combination thereof. Griffa is the Gyro Pilot from the second and third films
He looks a bit like him. And assuming Griffa actually exists and isn't supernatural, he has to be someone from Max's past. Gaspa Grope is Fifi
Before his boss battle, Top Dog Gaspa Grope taunts Max, saying "You think people still believe in heroes? Huh huh huh...", hearkening back to MFP Commander Fifi's line in the original film: "You say people don't believe in heroes any more? You and me, Max...we're going to give them back their heroes!". Fifi and Max had the conversation privately, so how else could Grope make that taunting reference? Plus, Grope's gimp getup is just one step up from Fifi's usual leatherman outfit. And it fits the plan George Miller once had to reveal the second film's Lord Humungous as a badly-burned, Face Heel Turned version of Goose from the first film. The events of the game never happened
With how the game ends exactly the same way the game starts, there is a solid argument that everything that happened in the game was all in Max's mind.- Interestingly, Max's prequel comic for Fury Road has some story elements from the game (such as Max getting a V-8 engine from Gastown, reclaiming the Interceptor and the deaths of Hope And Glory), but many others completely absent (such as Scabrous Scrotus, Chumbucket and the Magnum Opus).
Earth suffered a literal, Biblical apocalypse
The world ended when a bunch of terrible things happened at once. A global War erupted. A Pestilence that infected livestock killed anyone who ate them. That combined with all sea life "disappearing" and crops dying caused a global Famine. Death goes without saying.All of these horrible things (among others) happening at once is unlikely, but still Maybe Magic, Maybe Mundane. The biggest question is what happened to the oceans. They don't just "recede to nothing" in a mostly-modern, mostly-realistic setting like this. Perhaps it was the literal Horseman Famine or Death doing their part to end the world.
Now, the world is in a state where these four things are a way of life. Lunatics war with each other, many humans suffer from cancer or disease, food and water are rare, and people don't even blink at all of the death around them anymore.
