Technically the real piece they gave up was Hreschuk, who was a late 3rd round pick.
Also, Domi is just not that good of a hockey player. He may attract a bit of attention this year since he is playing a bit better with Chicago, and the options for good scoring forwards is a little bit weak unless you get your hands on one of the aging/oft-injured vets like Bertuzzi, Kane, JVR, ROR, Toews, Monahan, Nyquist, Drouin, etc. (and let's be honest, most of those guys are not playing particularly well right now and you are counting on them returning to form with better teams and better health). After those guys, it is pretty much just Domi and Barbashev before you start getting into Bjugstad, Ritchie, Sundqvist, Dadonov, Bonino, etc.... And none of those guys should be moving the needle on competitive teams.
You should arguably be more worried. Robertson's injuries were freak injuries that he can probably fix with improved skating balance (as long as he is not already broken from the injuries he has). Chychrun's injuries are far more serious and concerning... Arguably like Matthews but far worse.