TL;DR: No one curr, because humans have a lot of emotional inertia, and unless the original discoverers started using it to make sweeping changes, they'd have no incentive to care. (But see the teal deer below for some longer discussion.)
Like the question you linked, I think the ultimate answer might come down to "Not a lot of people would care, or change their behavior."
The thing is, unless you could prove to everyone, everywhere, instantaneously that what you'd discovered was the unalterable Truth behind all existence (perhaps pull up the man pages for the universe on the Moon?), a very large number of people wouldn't even hear about the discovery.
Consider first that even in a fully industrialized, first-world nation, "important news" about science and technology (which this would be, at first) doesn't disseminate very fast or accurately to the populace at large. Most people aren't interested, and most news reporters can't make a science story interesting without needlessly sensationalizing (and thus distorting) it. Granted, finding out the universe is a giant computer simulation would be a very "sexy" story to start with, but you'd absolutely have absurd misreporting on it right from the word "go", and you'd have people who'd just ignore that reporting because it's science and technology and they're more interested in what the Kardashians are doing, or the Super Bowl, or whatever.
Second, only a fraction of the human population actually lives in industrialized, first-world nations. Unless and until scientific knowledge of the universal source code is used to eliminate subsistence-level living and give everyone an SUV and a McMansion (or whatever else is deemed appropriate), most people have no incentive or means to notice what's happened in favor of continuing to eke out their lives.
[I think, whether or not the scientists who made the discovery immediately started using it for crazy stuff, governments would react immediately and profoundly negatively to suppress what was going on. It undermines their legitimacy completely if someone can just rewrite them out of reality. Unless it was a government project in the first place--in which case they would definitely suppress the information, but there might never be any reporting on it to begin with until something like Wikileaks came along! You may want to look at how information on various black ops and other clandestine government programs has gradually gotten released to the public, with the caveat that this is something unlikely to be declassified, ever.]
But suppose you managed to tell everyone all at once, before the governments of the world could stop you. Then what? Some possible options I can see are:
Deleteman's option of mass suicide. I don't think this particularly plausible on a wide scale (i.e. half the human race ups and offs itself) simply because most people wouldn't actually internalize "I'm a simulation, my life doesn't matter". A simple consequence of human solipsism is that, barring physiological and biochemical defects or a lot of emotional trauma, your life always matters to you, no matter how bad or strange it is. We're just wired that way, and philosophizing out of it to the point of killing ourselves is hard. Suicide is usually an emotional decision. But, for small groups of people and individuals, this undoubtedly would happen.
Large-scale rioting, set off by charismatic individuals. I can see two subtypes of this, but there's probably lots more: Subtype one is "THE GOVERNMENT HAS TO PROTECT US" from the possible malfeasance of the terrorists/the amoral scientists/pick-your-enemy using this new discovery to hurt people. Subtype two is "THE GOVERNMENT HAS TO USE THIS TO MAKE OUR LIVES PERFECT". Since you can now end world hunger with a few lines of code, why aren't you doing it? Right now?
No one cares, because they assume it's all just a fantastic trick. This is the one of the more likely scenarios in my mind, because humans have incredible inertia when it comes to being budged out of their comfort zones. Like 2, this could come in a couple of flavors: "Science is just messing with us, it's not true" versus "If it is true, what does it matter if no one does anything with it?".
As a closing note, before my obligatory opinion-and-follow-up-storybuilding questions, I want to say an idea like this (concerning the unreality of the physical universe as we experience it) has already been proposed and is in the process of being tested: It's called the holographic principle. You could perhaps extrapolate from how little most laypeople know about or understand that to how they'd respond to the universe as a simulation.
Warning! This next bit is opinion! I think the more interesting scenario that you didn't touch on--and one that's much more likely in my mind--is what happens if the original discoverers keep it to themselves and start using it to rewrite reality to their benefit? Given the power to become a god, I can't see even the most dispassionate, dedicated scientist just passing that up. So much the better if their initial understanding of the universal simulation isn't very good, and they start writing buggy code for it...
Honestly, I think the better story to be told here--or the first in a series of many stories to be told here--would be how the discoverers handle knowledge of their discovery. Is it ethical to start tampering with the simulation, knowing they could glitch everyone out of existence? Should they tell anyone? And so on. Much of how the world reacts depends on what these people do; I know your original specification was that they just demonstrate it's all a simulation and then immediately vanish from the world stage, but is that the most interesting possible way to handle things?