One wonders if there might be some mistake here since other instances in the text refer to being “destroyed from off (the face of ) the land/earth” rather than being “destroyed upon (the face of ) the land/earth”:
There is one reading that has simply off rather than from off:
This may be an error for from off; see the discussion under that passage. There are also three occurrences that refer to being “destroyed out of the land”:
A more indirect instance is found in an Isaiah quotation:
The multiple use of out of clearly indicates that such usage is fully intended.
In the case of Jarom 1:12, the closest language that would have been responsible for causing a supposedly original from off to be replaced by upon would have been in verse 8:
Yet intervening between verses 8 and 12, we have verse 10 (“they should be destroyed from off the face of the land”), which, one would think, should have counteracted any earlier effect from verse 8 of the less similar “spread upon the face of the land”.
The larger passage for Jarom 1:11–12 states that at this time the Nephites were kept from being destroyed, and this was because of the preaching of their spiritual leaders:
We should perhaps view the verb destroy in this passage as referring to a continual destruction, not the complete and total destruction of the people. In other words, the text in verse 12 is probably not referring to the complete destruction of the Nephites from off the land (as it warns of in verse 10) but instead to continuing and specific acts of destruction (which could ultimately, of course, lead to their complete destruction). Thus the text can read “they kept them from being destroyed upon the face of the land”.
There are a number of places in the Book of Mormon text where the verb destroy refers to a continuing destruction, not a total one, as in the following example:
As the children of Israel wandered in the wilderness for 40 years, the Lord gradually killed off all the adults who had rejected the advice of Joshua and Caleb and rebelled against Moses (see Numbers 14:26–39). This destruction was gradual and spread out during the 40-year sojourn. Nor was this destruction ever total since the younger generation was preserved and allowed to enter the land of Canaan. Thus 1 Nephi 17:31 can state without contradiction that the Lord did both “destroy them” and “lead them”. By interpreting the verb destroy in Jarom 1:12 as referring to a continuing and incomplete destruction, we can maintain the earliest reading of “being destroyed upon the face of the land”.
Summary: Retain the unusual (but apparently intended) usage in Jarom 1:12: “by so doing they kept them from being destroyed upon the face of the land”.