Obviously they were our weakest line by a good margin, but that's true for basically all 4th lines. Simmonds was -7 over 72 games, so a net -1 every 10 games. For that you get someone who fights and keeps the opposition a bit more honest. Obviously it's not guaranteed that Simmonds would have a similar +/- this year, or that his replacement would be even, but I think you'd be looking very roughly in that range - we're probably about 1 goal worse every 10-15 games with Simmonds instead of ZAR or Aube-Kubel.
FWIW, I have Simmer as the 13th forward. I wouldn't play him every game, but on games we think are likely to get chippy, he'd be in. On games we think will be less chippy, he'd be out (replaced by one of ZAR or Aube-Kubel). Basically an opponent-by-opponent decision (quite a common way to go with fighters). I'd probably play him in ~1/3 of the games.