Answer
No, Antigonus I Monophthalmus was not the last ruler of his dynasty. He was succeeded by his son Demetrius I of Macedon, who ruled from 294 to 288 BCE. Demetrius was then succeeded by his son Antigonus II Gonatas, who ruled from 276 to 239 BCE. The Antigonid dynasty continued to rule Macedon until the Roman conquest in 168 BCE.