In one embodiment, a device in a mesh network rooted at a root node receives a subroot selection notification. The subroot selection notification indicates that the device should function as a root of a sub-directed acyclic graph (DAG) were a power outage to occur. The device determines that a power outage has occurred. The device forms, after determining that a power outage has occurred, a sub-DAG that is rooted at the device by establishing one or more other devices in the mesh network as routing children of the device in the sub-DAG. The device joins the sub-DAG to a DAG rooted at the root node.