I think before this most recent injury (in the past few days-knee), he completely recovered from his previous injuries, so if this is only a minor injury, I do think Walker will be a reward late in the first round. But that's a big IF as you pointed out.
I think the problems with Walker are that:
1) He *hadn't* fully recovered from his previous injuries. He was playing at a high level, but he lost a lost of that Vince Carter athleticism that at one point had him projected as a top five pick; and
2) I don't think there will be time for teams to examine Walker's medical records related to this most recent injury in advance of the Monday deadline for withdrawal.
If Walker stays in the draft, I can see a team taking a flyer on him. However, I think it's unlikely that any team will give him a commitment to making him a first round pick, without first examining Walker and all information related to his most recent injury.