I wish him all the best in his recoveries. That injury was beyond brutal, but medical research has come a long way in a short period of time, and his rehabilitation and recovery is on schedule from the reports I have read. How far he falls will depend on his medical reports and how patient an NFL is willing to be, understanding that he will most likely miss his entire rookie season.
Regarding the Cowboys, they have basically given redshirts to players in the past, and I see no reason why the Cowboys couldn't do the same for Lattimore if he is available at a reasonable round.