In the season 6 teaser it looks like Rusty is going to end up being a vigilante killing Guild members while dressed like the green hornet (expect blue). Awesome! What do you think happens that turned him? Death of Dean?
Oh and the teaser brings up a quality question: flamethrower or rocket launcher?
I'm betting that it's whatever happens on Gargantua 2. My guess is that The Revenge Society goes too far in some way, leading Rusty to disregard Guild and OSI rules.
My guess is it's not Rusty; or, at least, it's not the version of Rusty we've been watching. We already know the Ventureverse is a multiverse from "Bright Lights, Dean City." If it is a Rusty, and not just a guy that looks like him, my guess is that it's not our Rusty, and one of the Rustys from one of the other universes is going around trying to make things better for the other versions of himself.
Our Rusty's defining characteristic in my view is an utter jadedness about everything he sees as a part of his weird life. Going on a Guild-member murder spree just doesn't fit him (either in temperament or in skill; being able to both perform and succeed in getting away with multiple murders just doesn't seem like something a guy with Rusty's general clumsiness, not to mention his various maladies, could do). Something would have to happen that is truly character-altering.
One of the boys being killed for the last time might do it, but that seems like a really big step for the show to take. And if they did, it'd almost certainly be Hank, just from a production standpoint; Jackson's one of the creators, and so he could drop voice-acting a particular character without a problem, but if you kill Dean, you're essentially ending Mike Sinterniklaas' role on the show unless you bring in a new character for him to voice. If he's being cut loose altogether, then this is a nice way to do it, but I doubt that's the case; the Astrobase seems like a pretty close-knit group (given how much of it Jackson and Doc do themselves, and how rare it is for there to be guest voice actors), so I doubt they'd just dump one of the guys who has been voice acting for them from day one.
Point is, TL;DR: I doubt it's our version of Rusty, if it's a Rusty at all; if it is, it's likely something like one of the boys dying (probably Hank) was the catalyst. But as I said, I doubt it's our version of Rusty.
Rusty was broken at the end of the last season. who knows what he's gonna end up doing. Maybe he's going around spreading "joy" with his best bud, Ted. They said possibly with a huge guy, lol, so if not Hatred.. though, I guess it could be Brock but it's not likely. Unless the OSi discharge Brock and left him hanging, I just can't see him going awol again.
Also, who says it's not the monarch? they look alike .. sh!t, what if it's the monarch and Rusty wreaking havoc because they found out they're half brothers. Big guy could just mean Tall guy.
You never know where they're gonna take the show. But I honestly doubt they'd kill off either Hank or Dean for real, not even Dermott since there's so much left to play with there. Hank and Dean are just too critical to the show.