Typically the wedding vows would be a variety of the lines
Willst du sie lieben und ehren (...) in guten wie in bösen Tagen, (in Gesundheit und Krankheit, in Reichtum und Armut ...) bis dass der Tod euch scheidet?
Grammar-wise this boils down to
Willst du sie lieben?
with lieben in infinitive because it belongs to the flexed verb wollen in the first position of the question.
More prosaic examples following the same pattern would be (randomly chosen):
Willst du fernsehen?
Sollen wir aufbrechen?
Kannst du aufstehen?
Now, when in your example the until death do us part has shifted its position (at the back is just customary), this does not influence the original meaning. Let's call the willst du sie lieben ... part A and bis zum Tod, der scheidet / bis der Tod euch scheidet B for simplicity.
Then you could either use the sequence A-B (as above), invert to B-A (albeit sounding a bit akward, but let's call it literary freedom) or even split A into A1 and A2 and stuff B into the middle, separated by two commas, leaving you with:
Willst du (A1), bis dass der Tod euch scheidet (B), sie lieben (A2) ...?
Which is the pattern of your question.