I think a good corollary question to ask that may reach the same answer for you would be: In any given country during the 1400s-1600s, When would a person be considered legally dead if they were lost out at sea (or beyond)?

A formal complete codified canon law is relatively recent (That Source says 1917, then 1983). Cuurent Catholic canon law covers the case in canon 1707:

PROCESS IN THE PRESUMED DEATH OF A SPOUSE

Can. 1707 §1. Whenever the death of a spouse cannot be proven by an authentic ecclesiastical or civil document, the other spouse is not considered free from the bond of marriage until after the diocesan bishop has issued a declaration of presumed death.

§2. The diocesan bishop is able to issue the declaration mentioned in §1 only if, after having carried out appropriate investigations, he attains moral certitude of the death of the spouse from the depositions of witnesses, from rumor, or from evidence. The absence of a spouse alone, even for a long time, is not sufficient.

§3. The bishop is to consult the Apostolic See in uncertain and complicated cases.

Canon 1141 has the general principle: "A marriage that is ratum et consummatum can be dissolved by no human power and by no cause, except death." (Followed by cases involving non-baptised people.)

Twenty-fourth Session of the Council of Trent, canon 5, says "Can. 5. If anyone says that the bond of matrimony can be dissolved ... by reason of the voluntary absence of one of the parties, let him be anathema."

The Council in Trullo, or Quinisext Council: the article says that the Catholic Church has never recognized this council of 692 AD. Canon XCIII is

If the wife of a man who has gone away and does not appear, cohabit with another before she is assured of the death of the first, she is an adulteress. The wives of soldiers who have married husbands who do not appear are in the same case; as are also they who on account of the wanderings of their husbands do not wait for their return. But the circumstance here has some excuse, in that the suspicion of his death becomes very great. But she who in ignorance has married a man who at the time was deserted by his wife, and then is dismissed because his first wife returns to him, has indeed committed fornication, but through ignorance; therefore she is not prevented from marrying, but it is better if she remain as she is. If a soldier shall return after a long time, and find his wife on account of his long absence has been united to another man, if he so wishes, he may receive his own wife [back again], pardon being extended in consideration of their ignorance both to her and to the man who took her home in second marriage.

The commentary wonders whether the Catholic Church would have accepted this and ends "Various scenarios are considered in Gratian's Decretum. (II, XXXIV, Q. I-II)". Someone familiar with Latin and what that citation means might investigate further -- I couldn't find a relevant passage quickly using Google Translate on pieces of Decretum Gratiani.

While I don't have a definitive answer, I think that the answer in a Catholic land would very likely be "without good evidence that the other actually died, never".

Unless, of course, the wife could get an annulment, but that would depend on a deficiency of the marriage that has nothing to do with the disappearance (evidence that one of them had already contracted marriage, say, or had been betrothed, or had previously had sex with someone too closely related to the other, or the marriage had not been consummated, or ...).

There was a top level comment referencing a 1603 law that I prepared this response to. I hope no-one minds if I let it stand:

This is just my drivel as I research around this point and the citation given.

The only legislation reported by the UK national archive (who manage legislation.gov.uk, formerly housed at statutelaw.gov.uk) between 1600 and 1606 is the Privilege of Parliament Act 1603 (and 2 Scottish Acts) -http://www.legislation.gov.uk/aep/Ja1/1/13. It regards punishment against parliamentarians being enacted when they cease to be members of parliament.

Matrimonial Causes Act 1973 [mentioned in the footnotes of the cited book at p.30] Section 19(3) puts in place an assumption of death for 7 years as a reason for ending a marriage. There doesn't appear to be any reference to that being legislation already standing.

... ah, hang on ...

"Labour History, Issues 74-75" appears to be the source, their source being a reference provided by an Alison Vincent: "1 Jacobi 1, c.10 and 11, 1603".

So I assume that's James' (VI | I) first statute ("Statuta Jacobi"); this reference (below) gives the title "An Act to restrain all Persons from Marriage until their former Wives and former Husbands be dead" as "Stat. 2 Jac. 1, c. 11." (dated to 1604).

Which is, Wikipedia tells me, the Bigamy Act 1603. Under the long title there is a transcript found at http://freepages.genealogy.rootsweb.ancestry.com/~framland/acts/1604.htm but without reference to the source used for the transcript.

Well that was quite a rabbit warren ...

In my travels I came across this - "Concerning those that divert from others, being joined of before in lawful marriage" - from the Records of the Parliament of Scotland, http://www.rps.ac.uk/trans/A1573/4/2 whereby James VI enacts that after 4 years separation the appropriate representatives of the "Kirk" (ie Church) can be called to admonish an absent spouse ultimately with excommunication this then being a reason for grant of divorce. Very interesting.

tl;dr if one said one's spouse had absconded it seems after 4 years (+ecclesiastical administration time) you could get a divorce (in Scotland, by 1573).

Question - when James VI took over as James I did all his former legislation get applied somehow?

Could someone point out the demographics for sailors, too, please?

I would hope for the couple that most sailors have been bachelors, otherwise I don't see the reasoning behind choosing such a profession.