I wouldn't count the OHL out. They might want him to work on his offensive game, for which the Owen Sound is likely the best option. If he goes back to Mannheim or comes to GR, he's not going to be on the #1 PP.
And it's not like the DEL is very far from the OHL, in terms of quality of play. The OHL is the best CHL league by quite a lot, and the DEL is maybe the 4th best European pro league? 5th, I guess, because the Czech Extraliga is pretty good too. And then there's the Swiss NLA, so maybe the DEL is 6th. Point is, the gap there is smaller than it seems, especially when we're talking skill level.