And that's where it's actually fun.
IF you were to sign this and IF they actually called you in for something it's pretty obvious that their H1-B guys and the Sun-Trust management are clueless as to what was done, so milk it. You have to be reasonably available -- which doesn't mean you have to lose your current job, so the only time you can work is at night, right? At night, with your feet on the desk and obviously struggling really, really hard over this intractable problem. "It's gonna take months, and months of work ex-boss. You better plan on this taking years of work, with you hiring me at consulting rates after the severance has run out. Oh, you don't think so, you think I should finish this faster? Then why'd you call me in if someone should do it faster?"
Dumping the "why the hell do you think I'd help someone who fucked me over" attitude, my guess is that Sun-Trust is trying to cover their ass. According to the article, the H1-B folks were shadowing the workers for a month or two, meaning that they've not really had a chance to see everything that the employees really do. So down the road when something that they haven't seen comes up (annual RedHat upgrade, or whatever) and something unique that their setup/software requires breaks they want to be able to come calling the ex-employees asking for help.
In a normal layoff due to rough times for the company, I don't think the ex-employees would fight those severance terms too hard. The thing is, when you're being replaced by less qualified H1-Bs for no good reason I think you'd be hard pressed to expect much cooperation. If it was happening to me there would be a decision tree that goes like this: (1) It's an easy fix, but it was a weird customization we had to do to make specialized software work -> "Damn, ex-boss, that's weird. I have no clue, it's been too long since I've been there for me to remember how we did that. I know it was something really strange, sorry." (2) It's a harder fix, requiring more than a day of customizations -> "Oh that. Yeah, I vaguely remember we used to have to have to heavily modify packages u,v,w,x,y,z with some wrappers and a bunch of new procedures. Of course, if anything else was modified in the environment it'd take even more changes and analysis. You're talking a couple of man-years since I don't remember everything we did and frankly your environment is totally different from where I'm working now. Sure, I can be "reasonably available" for consulting after my current gig. Did I mention that I'm working 60 hours a week, so "reasonably available" is maybe a couple hours a week late at night? Yeah, that might push out that couple of man-years worth of work, I suppose, why do you ask?"