I'll preface by stating that I am neither party in this scenario, but am indirectly affected and want some outside perspective.
Imagine you have an adult child that has has developed a serious health condition that will severely limit their life expectancy and over the last few years, has already severely limited their day to day life to the extent they need a lot of care.
Complications caused of their condition could kill them tomorrow, alternatively they could live another five years or so. What would you do in this situation:
During a lengthy hospital stay, the adult DC in question became extremely stressed/distressed and needed their family to advocate for them and felt extremely let down by them when they didn't and and was upset by their attitude, which they felt was put and shut up. The parents refuted this. As a result, the adult child erupted into a tirade, culminating in going NC.
If you were the parent, after a matter of weeks had passed, would you try to resolve things (maybe send a Christmas card or letter as a non inflammatory way of making contact) or would you hold your DC to their word and leave them to it?