Our 4th line really shouldn't be an issue once Hyman is back, we are going to see one of Mikheyev, Hyman or Moore on that line but for few games both Johnsson and Kappy should see some time on our 4th line, nothing is earned until you prove you have
What we really need to think about is team toughness (both mental and physical). Our offense is one of the best in league but we need to get better defensively. The roster we have is what we need to use properly (and nothing wrong with this roster) and every one need to understand their role(s), you can't score 5 / 6 goals every game, and even after scoring those goals you can not win every single game unless you take care of your own end.
After this season we are going to need money to add to our "D" as only Rielly and Sandin are signed from current roster. We have Mtthews / JT / Mitch and Willie playing on our top 2 lines (which is good enough to carry those 2 lines and I strongly believe that Mikheyev, Hyman and Moore, they all can play can play on these lines
Next season we are going to have about about $14 M at current cap ($81.5 M), assuming next year's cap hit go up by a million we will have close to $15 M in hand to spend. As I said earlier Hyman, Mikheyev, and Moore are quiet capable of filling in our top 2 lines with one of those playing on our 3rd line. If we trade both Johnnson and Kappy next season for drafts / prospects that would give us another another $6.5 M in cap hit. With $21,5 M cap (if utilize properly), you can certainly sign both Muzzin / Barrie (or any other quality "D") for say $15 M, the rest you can spend on signing Mikheyev, Dermott, a backup goalie, added toughness, PK and then you have some players ready that are waiting to be promoted
I really have nothing against either Kapanen or Johnsson, but it's all about team and our needs at certain areas. I understand both Johnsson and Kapanen can generate some offense but how superior they are as compared to Hyman, Mikheyev / Moore. Losing either or both Kappy and Johnsson is not as significant as compared to adding to our "D" and toughness. The offense shouldn't be a big issue with our big 4 earners