The described technology is generally directed towards lossless delivery of data when there are route changes, e.g., in an integrated access and backhaul (IAB) multi-hop relay network. When a route changes is to occur, the last unchanged node in a multiple hop route preserves the data (e.g., copies unacknowledged and unsent PDCP PDUs from the protocol stack corresponding to the radio link control layer of the failed relay hop, and populates a replacement protocol stack for the node in the new route with the preserved data. Also described is pre-emptive detection of link failure, which triggers a route change based on monitoring retransmissions to detect a deteriorating link, which can occur before complete link communication failure.