Barbarians disappear, leaving diplomat

[fire-eggs]

Barbarian groups appear and eventually disappear. The diplomat is being left behind and doesn't disappear. In the original, the diplomat disappears when the last attack unit disappears [not the same as when the last attack unit is destroyed!].

[iegik]

In the original, the diplomat disappears when the last attack unit disappears

Actually:

if it can reach an area far enough away from other civilizations' cities, it can disband itself prior to capture. — https://civilization.fandom.com/wiki/Barbarian_(Civ1)