Throughout this passage Oliver Cowdery tended to write should rather than the textually correct shall, as we can see earlier in verses 5 and 7 when he initially made this mistake:
For these two cases, Oliver caught his error virtually immediately (in each case, there is no change in the level of ink flow for the supralinearly inserted shall ). So here in verse 8, when Oliver wrote should, he first thought this must be a mistake (just like the mistake he had initially made in verses 5 and 7), so he corrected the should to shall (there is no difference in ink flow for this correction). But later, probably when he proofed 𝓟 against 𝓞, he realized that 𝓞 actually read should, so he restored the should (his second correction is with somewhat heavier ink flow). Note that the 1830 edition here in verse 8 reads should, not shall. The following verse also has should:
Thus we get variation here in 3 Nephi 9, two instances with shall and two with should. In each case, the critical text will follow the earliest textual sources.
Summary: Accept the variability between shall and should in the parallel expressions in 3 Nephi 9:5–9 that refer to the blood of the prophets and the saints not coming up any more unto the Lord; the first two instances read shall and the second two should.