They're pretty much at the point in their relationship where they don't even pretend that Nack won't betray them if he thought he could profit from it.
I guess its just their good fortune that the SAX currently don't have any money or anything else Nack might want.
Although... The SA-X do happen to be walking factories of exceedingly rare and (I can only assume) valuable Chozo technology. True though it's infected and thus unusable if you want to keep use of your mind, however, I imagine Nack could put on the right sales pitch to keep him independently wealthy long enough for him to avoid the inevitable assassins that will chase after him once people find out that their loved ones have been assimilated by the X.
This is all speculation of course... for NOW...
they already tried to assimilate him before, so if we take the one thing Nack actually cares about, his life, its in his best interests to help Samus and Chrono.
Maybe we should hope that he runs out of bullets by the time the battle is over. Though, he'll probably keep a bit of ammo in reserve for later.
Well you know there is the thing that guys like Nack, though they'd never admit it, tend to have morals, but just buried and repressed pretty far down in their psyche where they ordinarily lay dormant, sometimes indefinitely, however there have been documented cases these morals have been awakened (most often by loud and obnoxious anime characters) which then infect the host like a virus and cause him to do something really good often begrudgingly, and rarely out of any convenience, and 7 times out of 10 resulting in their own sacrificial death, however there have been cases where said subject has survived.
Um, I guess you'd call that less reviving the suddenly dead and more turning it into some kind of mood zombie, but you know what they say. "Any resurrection where your brains don't get eaten is-" wait...
Unfortunately, we don't have any loud and obnoxious anime characters. We just have a cuss-happy swordsman and a powered-armor wearing violent bitch. Wait, what's that noise? AHHHH! *Runs away before Samus can shoot me*
People like nate have morals, and pay attention to them, they use them as a light house to stay away from the shore.
Loyalty is completley foreign to Nack.I wonder why?Maybe he's so unloyal a time loop cause him to be unloyal at conception