A couple more (technical) details:
The client has a range of states for a given keep wall section (the T-Junction, Long Wall, Short Wall, Corner Tower etc.). We only use the fully repaired one (the one always used in season 1) and, once the section has been destroyed, the fully destroyed one. The sections usually have some damage indicators at 35%, 50% etc, those will not be used.
The holes and siege towers are part of the client side models, both are visible when the client shows "the most destroyed state" of a section, same for towers and the rubble. To simplify the whole process, once a wall section (or tower) reaches 0% we will make the client show the most damaged state, that means siege towers will appear if they are part of that sections "most destroyed state", or holes or the rubble. Certain sections, like the corner towers for keeps, don't allow access from the outside once destroyed, they might however give more line of sight into them.
The way line of sight works for NF keeps has been entirely reworked, previously the keeps were fully baked into the map, now there is an additional line of sight layer for the keeps of a given zone. Destroying an NF keep component (or tower) causes that nf keep line of sight layer for the relevant zone to be rebuilt. There might be a slight delay but in general it should not be noticeable (it takes around 1 - 2 seconds to rebuild the nf keep line of sight for a zone).
NPC pathing is still a work in progress, however, with the line of sight now done pretty much the same mechanic can be used for that but it's still quite a bit of work to make that happen.