This might be one of those "Silver Linings" moving forward for the Packers. I have been impressed by MVS and think Saint Brown is not that far behind. Both will continue to see more playing time. The other part of the silver lining, if the Packers want Allison back in GB for 2019 and beyond (his rookie contract is up after this season), I think he will come at a far cheaper price. Sucks for GMO but I think possible a win for the Packers. They could also reactive Kumerow now off the IR.
Allison will be a restricted free agent.
If he'd not been injured, at the high end they'd go with the second round tender. That means they could match any deal he gets elsewhere or decline to match and get a 2nd. round pick.. If there were no takers, which there wouldn't be at the cost of a 2nd. round pick, the Packers would pay him the mandatory second round tender salary. It was $2.9 mil for 2018 plus a bump in line with the % of the 2019 salary cap bump.
Now, assuming this is a serious injury, if they tender him at all I'd expect it to be under the right of first refusal option. In that case, the Packers have the option to match other offers. However, if they decline to match, there is no draft pick compensation. If there are no takers, the Packers would pay him 2018's $1.9 mil + the 2019 bump.
So, the difference between the high and low scenarios is about $1 mil for 2019, not a big difference.
Brice is also restricted under the same terms.
Patrick, Whitehead, McCray, Carson, Gilbert, Tonyan, Kumerow and Lancaster are exclusive rights free agents. They cannot negotiate with other teams. As the name suggests, the Packers hold exclusive rights. Clearly the team has a lot of leverage. I think it was the Broncos who paid their starting center from the previous year $700,000 under this provision.
All of the other free agents are unrestricted. They are free to sign anywhere. Of course, draft pick compensation is subject to the vagaries of the league pool's value determinations and offsets.
These various FA designations are taken from spotrac.com. I can't guarantee they are entirely accurate but I have no reason to believe they are not.