Drabek is certainly no lost cause at this point; he's still only 23 and clearly has MLB-caliber stuff. That said, he was a guy who was expected by many to be ready at this point, so this is definitely a disappointment for Toronto. 52 walks in 73 innings is just not a number you want to see from any pitcher, and it's not as though he had a ton of strikeouts offsetting it.
If I had to guess, I'd say Drabek is still probably going to be a very good MLB pitcher, but his control problems are a definite cause for concern. I think this does highlight some of the risk the Phillies would have taken on had they kept Drabek, as they would have been dealing with these growing pains much in the way they dealt with those of Gavin Floyd (who, by the way, is as good of a comparison as I can think of for Drabek at this point. The other guy who comes to mind is Brandon Duckworth, but I wouldn't wish that on anyone.)