I find it hard to think that Hayne could come back in on massive coin. He's had over 2 years off at this point, no? He's also spent that time training in a style that probably isn't very well suited for RL, NFL training is all about sprint and burst, not about endurance.
He'll need to completely re-train to get back in RL shape, now, I'm not saying that'll be hard for him, far from it, but it will still need to be done, and it essentially makes him untested in a way. Which should bring down his value.
Competing in the 7's will be actually be a good thing for him, and should get him get back into RL mode.
But no way I see him singing for $1m+ I'd say the $700-800K mark sounds about right as a max payment.
He'll get TPA out the arse too, so it's not like he'll have to hand around Chruch street mall asking people for 50 cents or a spare ciggie...