Neighbor's Retaining Wall Is Falling Apart Near My Fence

Location: Illinois (McHenry County). We purchased our house in 2017. The fence was installed before we moved in. One of our neighbor's yards is slightly elevated, and there is a 2.5' wooden retaining wall on the other side of the fence with about a 3" gap in between. The gap has been filling up with dirt, leaves, and bits of trash over time, and the fence has begun to sag towards our yard. I was going to drive in a fence post repair spike on the post that was leaning farthest, but the aforementioned debris made it impossible to push the post into a level position. I ended up removing an 8' section of fence between the posts to clean up behind it. Because it has been holding in so much moisture, the wall is rotting out (in addition to many of my fence rails which I ended up replacing before rehanging the section). It feels like a sponge in many spots, and chunks of it easily fell off when I (gently) scraped the dirt off with a shovel. I removed enough mess from the area that I was able to push the post back to normal, drive in the spike, and rehang the panels. Both the wall and the fence likely do not have much life left. My question is, should the wall collapse, who would be responsible for the damage, especially if it took my fence with it? I think it's safe to assume that the fence was put in after the retaining wall. The houses in my neighborhood were built around 1996 so the wall is probably the same age. It may be worth mentioning that we have an above ground pool and local ordinance requires that we have a fenced yard for it. Also, the neighbor's row of privacy trees (possibly arborvitae) above the wall were planted sometime after 2017 and have grown significantly since. The center of the trees are only around 18" from the edge of the wall and maybe 2' from our fence.

https://imgur.com/a/3OjSSLQ