Well...obviously you can't figure things out this way, and I think that there may even be a tongue in cheek element in this conversation.
However, I don't think it's the goal scoring that will be the notable difference sans Kessel. I think it's the playmaking, focus of the offence aspect that'll be slightly missed and will be a bit tough to replace. If Kadri is the likely replacement as the offensive catalyst, we know he doesn't have Phil's offensive abilities yet (just talking offence, we know he has better D). So how is JVR affected? We're not sure. What happens with Bozak if he remains on this team? Who the heck knows. How many more goals will a Parenteau, Lupul or Glencross score (than their previous season's totals) getting a lot more time on a first or second line with pp time? It's all wild speculation at this point.
I think with all of the changing variables, in the end, we score just as many goals. But who the heck knows?