Robust routing protocols are crucial for ensuring reliable data transmission in flying ad-hoc networks (FANETs). Existing routing protocols for FANETs primarily rely on the global positioning system (GPS) or other external positioning systems. However, there are numerous GPS-denied mission scenarios where FANETs must self-locate to perform tasks, rendering conventional GPS-assisted routing ineffective. To address this challenge, this paper introduces an integrated sensing and communication (ISAC) enabled proactive routing protocol for FANETs. Generally, ISAC enhances efficient self-location within a FANET, and such topology awareness is vital for robust routing. More specifically, beyond the conventional unified identifier (UID) in the digital domain, we propose an ISAC-enabled spatial-grids identifier (SID) that encodes mobility information in the physical domain. The ISAC-enabled SID serves a cross-layer function in FANETs: facilitating routing at the network layer and guiding beamforming at the physical layer. By leveraging ISAC and the dual-domain identifiers, we propose a proactive routing scheme that is effective and resilient to the highly dynamic topology changes in FANETs. Simulation results demonstrate that the proposed routing protocol significantly reduces routing overhead and transmission delay, enhances packet delivery reliability, and optimizes overall network performance in FANETs.