6 The verb is רִיב (riv); it is often used in the Bible for a legal complaint, a law suit, at least in form. But it can also describe a quarrel, or strife, like that between Abram’s men and Lot’s men in Genesis 13. It will be the main verb behind the commemorative name Meribah, the place where the people strove with God. It is a far more serious thing than grumbling—it is directed, intentional, and well-argued. For further discussion, see J. Limburg, “The Root ‘rib’ and the Prophetic Lawsuit Speeches,” 88 (1969): 291–304.
7 Heb “and they said, saying.”
8 The particle לוּ (lu) indicates the optative nuance of the line—the wishing or longing for death. It is certainly an absurdity to want to have died, but God took them at their word and they died in the wilderness.

In other versions

And the people quarreled with Moses and said, “Would that we had perished when our brothers perished before the Lord!

They quarreled with Moses and said, “If only we had died when our brothers fell dead before the Lord!

The people quarreled with Moses and said, “If only we had perished when our brothers perished before the Lord.

The people blamed Moses and said, “If only we had died in the Lord’s presence with our brothers!

And the people quarreled with Moses and spoke, saying, “If only we died when our brothers were dying before Yahweh!

And the people chode with Moses, and spake, saying, Would God that we had died when our brethren died before the Lord!

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