The United States is run based on the text of the Constitution, of the general body of law, and, even more unfortunately, assorted legal precedents.
It is not run based on dying wishes.
What Justice Ginsburg’s dying wish was and whether it’s authentic or not has zero relevance to anything involving her seat. A dying senator would not be entitled to have his seat remain vacant. Ditto for a dying president.
There’s no reason for a dying justice from the third branch of government to be able to do so.
Dying wishes are to be respected only insofar as they don’t interfere with the legal rights and obligations of the country. The people of the country have a right to be represented in the legislature and in the executive branch, and in the judiciary. Cases that go before the Supreme Court should be heard by a full court.
That’s how the system functions.
Now a sensible alternative to this mess (if there was a market for sensible alternatives, which there isn’t) would be formalizing and codifying rules for replacing deceased justices in law, rather than usage and custom, which is what it is now, and possibly having alternates in place. All of that is a non-issue because this is a brute force power struggle. And if President Trump succeeds in filling a court seat, and Biden wins and Democrats take the Senate, court packing is on the agenda.
And the dying wish becomes another political banner to wave.
Everyone knows that if Justice Scalia’s family had communicated a dying wish not to have his seat filled by Obama, it would have been dismissed by Democrats and their media out of hand. And they would have been right to do so. There might be good reasons to fill or not to fill a seat, but a dying wish isn’t one of them.