I think people romanticize around Heed. His lack of footspeed/positioning has been exploited on a couple of occasions and I don't think the coaching staff trusts him defensively. If memory serves it was right after he got walked by Virtanen on that end to end goal that he got banished to the press box (see the YouTube video of you need a reminder of how bad that was).
It is a bit telling that on one hand you confidently claim that playing Demelo during crunch time was the difference in having home ice, but on the other call the coaching staff idiotic for not playing a rookie on his off side based on conviction with no reasonable basis that would have been better.
It's telling how you mentioned that one play by Heed, when there were a ton of plays where Demelo has been slow or fumbled the puck that led to them being hemmed in the d-zone for an extended shift this recent stretch. Or his giveaway that directly lead to Minnesota's OT goal earlier in the season. Or his poor positioning on the first 3 goals of the latest Minnesota game. Yet, unlike Heed, for some ridiculous reason, he isn't being benched for them.
Even if there was a difference between Heed and Demelo defensively (there isn't none), what Heed brings in puck movement and offense more than makes up whatever difference you might think their defensive skill is.
Ryan being on his off-side would take some adjustment (which could have been experimented these last few games of the regular season), but the fact that he does
everything better than Demelo, the change would be worth it. He's also been defending on both sides fairly frequently when paired with the roaming Burns. The only real "trouble" would be keeping the puck in the zone on his off-hand, but that's an easy adjustment.