The problem is that in the Marriage sentence there is no variable which can link to a Principal's "other" spouse. (If they had several spouses, it would be an issue of "which" other spouse.) I know of no way to do this other than by manually entering the name of the deceased "other" spouse as text for the sentence.
My habit for such text is to use split memos, and reserve one of the memo parts for this specific text.
For example, I have some other uses for [M1] and [M2], but might reserve [M3] for a deceased spouse of the Groom and [M4] for the deceased spouse of the Bride.
So the "Female" (or Role "Bride") sentence might be:
[P] married [PO]<(widower of [M3])><[PARO]><[M1]><[D]><[M2]><[L]>
And the "Male" (or Role "Groom") sentence might be:
[P] married [PO]<(widow of [M4])><[PARO]><[M1]><[D]><[M2]><[L]>
Then all that would be needed is to enter the deceased spouse's name in the appropriate split memo part, such as:
in a ceremony performed by Fred Smith, Minister of the Gospel, at 4 in the afternoon||at the home of the bride's parents||Sarah Baker||John Brown
The female sentence output would look something like:
"Sally Green married Harry Brown (widower of Sarah Baker), son of James Brown and Harriett Frost, in a ceremony performed by Fred Smith, Minister of the Gospel, at 4 in the afternoon on 19 Jan 1946 at the home of the bride's parents in Ferndale, Oakland County, Michigan."
This might be a good example where the new ability to have Reminder text specific to a particular role probably would be useful.
Hope this gives you ideas.