Dance did not plan a sacrificial last stand

Were Dance's leading East Indiamen meant to sacrifice themselves so the rest of the convoy could escape?

No; although they could have become a screen if necessary, Dance intended their aggressive bluff to drive the French squadron off.

A viewer suggests that the apparent escort could have served as a distraction while the rest of the China Fleet escaped. Such a result was possible, but it was not Nathaniel Dance's plan. Dance intended the selected merchantmen to act with maximum aggression for roughly an hour and convince Linois to withdraw. Their role was an active bluff designed to preserve the whole convoy rather than a knowingly doomed rearguard action.