Fences and Walls: Retaining Wall in Slow Moving Landslide Area

My question involves real estate located in the State of: Hawaii

Facts:

Purchased home in 2015. After purchase, property survey was conducted. Survey showed the left bordering retaining wall (approximately 6ft in height) mostly inside subject property parcel. A portion of the wall was 0.5ft outside the property line. This section of retaining wall was reconstructed by subject property owners in mid 2016 to correct the 0.5ft encroachment and as part of maintenance.

Very recently, a new survey was conduced showing this wall 0.9ft outside subject property boundary. Land movement is severe and stabilization of this retaining wall will be very expensive and/or impossible.

Question #1: When retaining walls are once within a subject parcel, but later slide into the adjacent property, does the ownership of the wall change from subject property ownership to adjacent property ownership?

Questions #2: If the major part of a hillside is moving and it's assumed that all lots are moving proportionally to the landslide, how are the property boundaries determined? In the example above, is the subject property owner responsible for taking down the now encroaching retaining wall and moving it to within the subject properties boundaries? What if moving of the wall becomes too close to the subject properties house? Would the house (or a portion of the house need to come down)?

Thanks,

Fences and Walls: Retaining Wall in Slow Moving Landslide Area