Do Soraka and Karthus ultimates interact with people in Death's Realm?

New Mordekaiser ult looks awesome but these couple of interactions I would like to know more about, considering Karthus does 8 billion damage and Soraka R could save Mordekaiser or his victim pretty easily. Are they untargettable by these abilities as well? Also, does Yuumi stay with someone if Mordekaiser ults the person she is attached to?
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