Wordreference topic about subject

https://forum.wordreference.com/threads/till-death-do-us-part-does.2561856/

The expression till death us do part and its variants dates back to the 16th century at least;

1) Till and until are synonyms. The word till without an apostrophe is perfectly correct, is perhaps preferable to 'til, and is vouched for by every dictionary. The word 'til is considered perfectly correct although historically, till is not a contraction of until, it's exactly the other way around--till came first.

2) The language is from the Anglican (Church of England) Book of Common Prayer, "An Order for Marriage." Because the Book of Common Prayer has gone through various editions, I'm not absolutely sure about the age of the language. The very first edition was published in 1549, making it older than Shakespeare and "the Bible" (i.e. the King James version). 

3) An Episcopalian (U.S. branch of the Anglican church) website gives two different versions on its website; the second is obviously older:

In the Name of God, I, N., take you, N., to be my (wife) (husband), to have and to hold from this day forward, for better for worse, for richer for poorer, in sickness and in health, to love and to cherish, until we are parted by death. This is my solemn vow.

 or this

I, N., take thee, N., to my wedded (wife) (husband), to have and to hold from this day forward, for better for worse, for richer for poorer, in sickness and in health, to love and to cherish, till death do us part, according to God's holy ordinance; and thereto I (plight) (give) thee my troth.

Though it is an archaic expression, it's so well known that there was a BBC sitcom in the 70s or 80s named after it. I think that I said it in my marriage vows a few years ago.

There are several hundred archaic expressions from the King James Bible and Shakespeare which live on in modern English, sometimes in their original form (like this one), and sometimes modified.

Language of KJV had also been archaic at the time KJV was printed

So Book of Common Prayer (a source of the phrase) also  uses archaic language. Maybe because it sounds cool.