Very happy that you have received your end of the trade! Even if it did take a while.
I feel quite lucky with my experiences that I've had here in comparison.
I do remember having personal problems when I did a swap with someone here on the Arena and I felt awful about being absent and a post was started about me and I felt so embarrassed. Although I did get in contact and sorted it all out and they were understanding and nice about it in the end! Even on the thread which really helped!
I do think you should probably leave neutral feedback, just as a warning to others. If they aren't planning to be active it shouldn't really bother them too much anyways! Just would save others any hassle and may keep the person on their toes in the future, its never nice but it can just be necessary
Congrats on your rare pony anyways