If McGahee still got drafted in the first round with the Bills knowing full well he likely wouldn't play that season, I think Lattimore still gets taken if not the first round, the second. There are plenty of teams willing to take chances on a potential pro-bowler. As a Jets fan, if we have a mid-1st or even if we are early and trade back and take Lattimore, I'd be happy with the risk. How many 1st round RBs get injured or bust with a healthy collegiate record?
Guys like Lattimore are very rare and well worth the risk, if he decides to enter the draft I'd be absolutely shocked if he is still there in the third round. If he didn't get injured last year or this year there'd be serious debate about him getting taken with the #1 overall pick (considering how the QBs in the class have been lackluster at best).