I read somewhere recently that HISMs will be phased out. PCG seems to switch to ISM for Nanite meshes if you’ve selected HISM - seems like ISM is the way to go - just don’t remove instances, move them to way below the level and reuse them if need be later.
Edit: In UE5.3 the UInstancedStaticMeshComponent has a bool “bSupportRemoveAtSwap” which you can set to true to swap the index with the last in the same way as HISMS.