That's a solid $13 million dollars that they're going to have coming off the books, and none of those guys are under the age of 32. Add in Oduya's $3.75 million, you're looking at almost $17 million to replace 5 players. The only forward of that group that I'd expect to get a raise from their current salary is Hudler, and that's because he's being criminally underpaid for what his production was in Calgary.
Holes, definitely, and adding in Nichuskin, you can definitely worry about them a little bit - but this is a team with Benn, Seguin, Spezza, and Klingberg all signed long term... players will see that and want to join them. Whether it's retaining the guys mentioned, or signing different players - they'll be fine. Then, in 18-19 when both of their goalies become free agents, they'll have another $10 million to spend on more talent. That team could change dramatically in a couple of years, and it could look even better than it already has.