The survival of this Berserker Clone was unprecedented, although this was not only due to the ingenuity of this Clone, but seven other reasons.
These seven reasons were the seven Children of Ruin, they had been for a while now, appearing when he was on the verge of destruction and saving him, they had not left his side ever since.
After the Children of Ruin left Rowan they had somehow found a way to reach his Berserker Clone inside the Underverse and they were the primary reason this clone had survived for so long. It was unknown how they had been able to find this clone, but they did, and their help had been invaluable to the Berserker Clone as he was able to reach places that his level of power would not accommodate.
Perhaps the Children of Ruin thought with their intervention, Rowan might view them in a more favorable light, but Rowan's thought was largely unknown, and so they followed the clone deeper into the Underverse.