Matt Harvey's Tommy John surgery will most likely result in him not being able to pitch all season, which is a big loss for the Mets' pitching staff. Thankfully, they should still be able to have a solid starting rotation this season, with Dillon Gee, Jon Niese, Zack Wheeler, Bartolo Colon and Jenrry Mejia all currently in the rotation.
Starting pitching has been a strength for the team and, unless any more significant injuries occur, should continue to be a strength.
In the bullpen, the Mets have lost Bobby Parnell for the season due to Tommy John surgery of his own. This means Jose Valverde will pretty much become the new closer, and Scott Rice and Jeurys Familia will be among those who will get opportunities to be New York's setup man.
The Mets' bullpen will not be the same without the presence of Parnell, but Valverde has been a very successful closer for many years and could more than certainly fill the void there. If the rest of their bullpen is effective, they should be able to preserve more leads this season.