"I, ___, take thee, ___, to be my wedded husband/wife, 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 pledge thee my faith [or] pledge myself to you."
"In the name of God, I, ______, take you, ______, 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 health, to love and to cherish, until we are parted by death. This is my solemn vow."
"I, ___, take you, ___, to be my husband/wife. I promise to be true to you in good times and in bad, in sickness and in health. I will love and honor you all the days of my life."
There are many versions of wedding vows. The Hindus and Muslims may have a different way of saying it than a Calvinist might, but in all of these different versions, there is one constant, five words inserted near the end that change the outlook on it. 'Till death do us part'. This pledges a lifetime of all of those things. It does not allow room for "ifs", "ands", or "buts".
When someone dies, as a symbol of reverence. It is done to give the dead body dignity, and show that they are sleeping peacefully. It is a show of respect that is often awarded to the spouse to bestow. When you make the vow "till death do us part", you are telling them that you will be there to close their eyes. You will be there to make sure that they are cared for after death, and they, in turn, are making the same vow to you. There is no way that this vow could mean anything other than a promise to close the eyes of your beloved when they pass from this bleak world.
No matter what denomination or religion you come from, there will be some version of "till death do us part". That can't be a coincidence.