Here in the manuscripts, there was a persistent tendency for Oliver Cowdery to omit the and before the present participial clause that ends this sentence. In the original manuscript, Oliver inserted the and inline, although the and (written as an ampersand) is raised somewhat off the line. The correction is virtually immediate since there is no difference in the level of ink flow. In the printer’s manuscript, Oliver once more omitted the and. This time his correction is a supralinear &, and it is written with a somewhat heavier ink flow. In this instance, Oliver probably caught his error when he proofed 𝓟 against 𝓞.
Of course, in English we do not expect a connecting and for a sentence-final present participial clause unless it is conjoined to a preceding present-participial clause, as in the following example:
But there is no such preceding present-participial clause here in Alma 49:27, with the result that the sentence seems to end with a disconnected nonfinite clause. Thus Oliver Cowdery twice omitted the and in the manuscripts, at least initially. Similarly, the editors for the 1920 LDS edition removed the seemingly unnecessary and in this passage. Yet elsewhere in the earliest text, there are a number of cases with precisely this construction:
Not surprisingly, editors have tended to remove this nonstandard usage. For the specific changes, see the discussion under Mosiah 23:13–14. The critical text will restore the original reading in all these cases, including here in Alma 49:27, since textually the and is fully intended.
Summary: Restore in Alma 49:27 the original and that introduced the sentence-final present participial clause (“and swearing with an oath that he would drink his blood”).