If Murphy was coming over in the morning Harry wouldn't have been so depressed.
He might be if some combination of Ebeneezer, the Alphas, Mac, Ivy, a bunch of innocent bystanders, Sanya, Butters, Mort, his warden friends, etc. died, and his brother was pretty close to the functional equivalent of dead, which he is. Your just assuming the only way he'll be depressed is if Murphy died. I disagree. Murphy's death is a sufficient, but not necessary, cause of Harry being depressed. Therefore, Murphy not being there isn't evidence that she isn't coming over or is dead. You're saying the fact that Murphy isn't there supports the statement that Michael and Charity wouldn't object to Harry's girlfriend sleeping over because the only reason she wouldn't be is because she's dead. You're saying that to support the proposition that if Murphy isn't there it's because she's dead.
You assert four premises and a conclusion.
Premise 1: Michael and Charity wouldn't object to Murphy spending the night sending the message that premarital relations are okay.
Premise 2: Murphy would be there if she were alive.
Premise 3: Harry would only be depressed if Murphy died.
Premise 4: Murphy isn't there.
Conclusion: Murphy's dead.
I reject premises 1, 2, and 3. Premise 3 is nonsense. Premise 2 has no support beyond wild conjecture. It would require Murphy not wanting to stay at her home, her not wanting to spend Christmas morning with her family, and Murphy wanting to be there for Harry and Maggie's first Christmas together all to be true. Premise 1 depends on the house being having extra room and Micheal and Charity to be okay with a boyfriend and girlfriend sleeping under the same roof when there isn't much of a reason for it. I agree with premise 4 because I reject premise 1, but we don't have definitive evidence that she isn't there.
Also it is a large house, at least two of the kids have left home.
I addressed that point.
Additionally, they might have a full house already with all the kids back for Christmas. Especially if any of the older kids have gotten married.
Even if all the bedrooms are full, there still is Charity's sewing room where they used to put Harry when he was injured, the floor, or a sofa.
You mean the room Maggie's likely to be sleeping in?