The convergence of integrated sensing and communications (ISAC) with reconfigurable intelligent surfaces (RIS) and metasurface-based architectures is emerging as a key direction for sixth-generation (6G) wireless networks, supporting joint communication and sensing through programmable electromagnetic environments. This survey provides an integrated treatment of metasurface-empowered ISAC across terrestrial, airborne, and spaceborne tiers. Six metasurface architectures are covered: passive and active RIS, simultaneously transmitting and reflecting RIS (STAR-RIS), space-time-coding metasurfaces (STCM), holographic multiple-input multiple-output (MIMO) surfaces (HMIMOS) and the closely related stacked intelligent metasurface (SIM), and metasurface reflectarrays that generate orbital angular momentum (OAM) beams. The survey reviews the electromagnetic foundations, channel models, ISAC waveform design, and performance bounds, then synthesises the terrestrial pillar across beamforming, resource allocation, hardware impairments, and energy efficiency. The OAM-ISAC pillar examines how vortex beams provide additional degrees of freedom for rotational sensing, while critically assessing the practical mode limits and maturity gaps. The non-terrestrial pillar addresses low Earth orbit (LEO) satellites, high-altitude platform stations (HAPS), and unmanned aerial vehicles (UAVs), covering link-budget, Doppler, and handover challenges. Cross-cutting enablers, namely artificial intelligence (AI) driven optimisation and physical-layer security, are surveyed with emphasis on their interplay with metasurface-ISAC. Two assumptions that pervade the surveyed optimisation literature, perfect instantaneous channel state information and cost-free channel acquisition, are examined critically: a coherence-time-aware accounting of pilot overhead, illustrated by an anchored numerical sensitivity analysis, shows that the reported multiplexing and sensing gains of large surfaces are bounded by the associated acquisition costs. The 3GPP, ETSI, ITU-R, and O-RAN standardisation status frames the route to deployment. Fifteen prioritised open challenges and a technology roadmap to 2035 complete the treatment. By bridging the electromagnetic, signal-processing, and networking communities, this work aims to serve as a reference for researchers and engineers shaping 6G ISAC.