Yeah he "bailed"
Dude was legit good enough to play for the sens last year and this year. Miles better than Zack Smith. They were so focused on him scoring goals that they failed to see what they had. Same thing with Pageau last year look what happened this year. They got pigeonholed because of their size and people overlooked their skills both on and off the puck.
The Pageau example is perfect. He stuck to it, kept working hard and listening to coaches/management, and now I believe has shown himself to be a permanent NHLer. Hoffman did the same thing, he stuck around and waited for his chances and finally capitalized - he even signed a 2-way deal. None of Hoffman, Stone or Pageau were just handed their spots, they all were given several chances to earn one through their play and all eventually did just that. All three are going to get paid this summer and get some job security.
Da Costa had some good spurts last year and got very close, but yes - he bailed on the process and has nobody to blame but himself. I have nothing against the guy, hopefully he comes back and fixes his mistake, but its ridiculous to just blame the team for not handing him a spot over other guys who were willing to pay their dues.