Dr. Robert Anderson (top foot & ankle guy globally, and who BTW recommended Cam not have surgery) makes detailed comments about Lisfranc ...
His specific comment on recover time was: "There are situations where the Lisfranc needs to be operated on. If the joint is out of place or has a bone injury or has significant instability, then those are reasons for surgery and surgery is basically done to stabilize those joint injuries with a combination of screws or metal plates. That can take 5-6 months to recover from surgery."
Cam's foot is fine and has long since healed. He has been posting strenuous workout videos with no limitations to social media for months.
...but given the previous Dr. rec's it's clear that on the severity spectrum the starting point of Cam's specific situation was lesser, thereby implying an even shorter recovery time.
Physically Cam is healthy as a horse, if he doesn't stick with the Patriots it won't be because of any lingering issues with shoulder or foot.