I know multiple people who have had Plantar Fasciitis. It is painful, but you can come back from it with steady treatment and care. My wife runs marathons and triathlons. She had it, was diligent about treatment, and was running again in 3 weeks. She started running before she was pain-free, but there's a point where the Dr will tell the patient that they aren't at a risk for further damage, just need to deal with pain.
Obviously, it depends on severity, but Byrd has been out for a while, and he clearly is waiting as long as he can. He basically doesn't give a **** about the team, and is milking it for all it is worth. He played on it last year when it was worse.
I partially blame his agent, who is biased because he gets to share in Byrd's payday. He also probably told him he'd be the highest paid S in the NFL, and that would not happen in any galaxy. If someone wanted to pay Byrd, they would have traded for him.