This position paper explores how future 6G Integrated Sensing and Communication (ISAC) technology can enhance U-space services, such as e-registration, geo-awareness, and tactical conflict resolution, for cooperative UAVs flying Beyond Visual Line of Sight (BVLoS) at low altitudes. We investigate two critical scenarios: GNSS failure and network outage, each addressed through dedicated workflow procedures that link relevant U-space services to safety and continuity requirements. By enabling real-time RF sensing, telemetry, and vehicle-to-vehicle communication, ISAC provides a scalable foundation for secure UAV integration in fragmented airspace, where traditional systems and current standards fall short.