Harlaw did not end the Crown's fight with the Lords of the Isles. In 1429 Alexander of the Isles, Donald's son and successor, burned the town and besieged the castle of Inverness. Pursued by a royal army, he fled to Lochaber where his Lochaber allies deserted him, and he was forced to surrender. Three years later a force led by Alexander's cousin, Donald Balloch MacDonald, bore down with his islesmen upon the clans of Lochaber, wasted all their lands with fire and sword, and defeated a force under the Earls of Mar and Caithness at Inverlochy. Among those killed were Donald Bronnach (the Portly) of Letterfinlay, son of Gilles (the youngest of the Three Brethren), and six of his seven sons. The youngest son, John, "not being able, or rather disdaining for MacDonald's cruelty to live in Letterfinlay, assigned his hereditary right to this land to a "Cameron" who was an uncle by marriage. The "Cameron" was MacMartin of the Clann mhic Ghillemhaoil branch of the Old Clan Chattan.
Gilles' surviving grandson moved to Rimore of Badenoch in Rothiemurchus, where the third branch of the Clan Macpherson maintained itself for three generations before moving to Invereshie in Badenoch. Thus it appears that the final migration of the Clann Mhuirich to Badenoch was a result of the revenge taken by the Islemen against the Old Clan Chattan of Lochaber for their desertion of the Isles and their adherence to the king.