Okay so if there's a cap crunch, you're actually advocating for a defense core of this for most of the year:
Toews - Makar
Girard - EJ (assuming he doesn't retire)
Lindgren - Malinski
That core is one injury away from being very weak, and it's already not very inspiring. The solution of course would be to acquire Manson's replacement in the offseason, but even if they traded for Peeke, that's less than 2m in cap savings, and I think Manson to Peeke is more than 2m worth of drop in play. I suppose you could assume 50% retention, but then this is getting expensive, which it would already be for all the guys you listed. Speaking of which, most of the guys you listed are not really options unless LTIR frees up cap space, since if we're trading Manson we're right up against the cap. And if LTIR frees up cap space for one of these guys, it probably means an important player is hurt, which means we need to replace that player too. I just don't see how it's really feasible to replace Manson next year. The year after, sure - one of those very guys you listed could get signed as a short or long term replacement. But I think you have to stick with Manson next season and lose someone else (if Landy is back). If it's not Girard, then it has to be either letting Lindgren (or Nelson) walk, or trading Coyle.
Nemec and Clarke are indeed interesting (especially Clarke), but not as Manson replacements. If we're trading him, our #1 need immediately a big guy who plays physical and can move the puck, who ideally shoots right. We would not be able to afford spending our rather meagre assets on yet another puck mover who can't clear the front of the net. It could be interesting if we end up with Lindgren and another physical LD if we trade Girard (Xhekaj for example). Then we could roll Lindgren with Malinski and the new guy with Nemec/Clarke as the bottom pair. This assumes continued growth from Malinski though.