We've been pretty fortunate - Leddy's current situation excluded - with injuries. That probably won't last. With the injuries to our depth guys in Bridgeport (Aho, Hickey, etc.), I'm not sure we can even afford to send him to the WJCs. Assuming the team is resigned to the fact that he's going to get his 9+ games with the team at some point this season, I think you just keep him here as the 7th defender, roll him into the lineup every 3rd/4th game - even when everyone is healthy - and have him for that inevitable injury(ies) that always pop up. Even if he's sitting at times, he'll easily get 35+ games over the course of the season. That's perfectly fine for a 19 year old.
He'll gain more valuable experience practicing and traveling with the team even if he's not playing every day than he will at the WJC playing first pairing minutes.