I was curious, so I decided to look up and see how many players who scored at least 3 points in their 9 games as 18/19 year-olds were sent back to junior.
Since the lockout season, I could only find 3 players:
- 2005-06, Gilbert Brule scored 2 goals and 2 assists in 7 games with Columbus before being sent back to Vancouver.
- 2005-06, Wojtek Wolski scored 2 goals and 4 assists in 9 games with Colorado before being sent back to Brampton.
- 2011-12, Brett Bulmer scored 3 assists in 9 games with Minnesota before being sent back to Kelowna.
All the rest were either sent back to junior with fewer than 3 points, or they were kept in the NHL (I didn't count Sven because he was an emergency recall and had to be sent back).
As long as he doesn't regress over the next six games, I don't see how Monahan doesn't spend the season in Calgary.