I'd place more attention on the 4th line personally. Tampa's 3rd line (or namely Paul) was the difference maker in the last game, but our 3rd line was huge in our Game 3 win.
Our 4th line was just out there taking shifts. They did practically nothing, and were a net negative in the end. Tampa's 4th line was effectively the same, but that is no excuse for our 4th line. Our 3rd line was at least an effective shutdown line and did provide some timely offense.
If we get our prospects to step up and help form a solid 4th line, that may be the difference for us. Keefe then needs to trust them throughout the game so they don't just play 7 or 8 minutes. Blackwell, Simmonds, Thornton, Spezza (except against MTL), Clifford, etc. have given us absolutely nothing over the years, or have even actively cost us games. It doesn't need to be expensive (after all, Tampa's 4th line is pretty much a bunch of sub mill guys), but even if they provided one or two more timely goals, we are winning series here.
Hence, we need to trust our prospects. They are cheap. They have skill. They have hungry. It is time to let these guys have their shot at replacing some of the guys we will need to cut.
I wouldn't say he is untouchable. But I don't think they are going to give him away for scraps, and good on them.
Unlike Leafs fans, our team actually values the importance that he brings to this lineup. It doesn't make him irreplaceable or untouchable. But it does make him a guy you don't sell for a mid-round pick either.