Personally, I went 3 and a half years without any SI, but then my mental illnesses started escalating and caused me to self harm again. I think with the right extended treatment it is possible, but I also that think everyone is different so it might not be possible for you in particular or any other individual who is struggling with SI.

I actually got over it when I was 16 (the start of the SI-free 3 and a half years) because it just stopped doing anything for me. It stopped giving me the release I needed when I was stressed or upset or guilty or depressed (or whatever else made me want to reach for something to injure myself with). And that was actually upsetting for awhile because I had no idea what else to do to help with my problems, but eventually that passed and I didn't think about it for a long time. So maybe if I hadn't become depressed and anxious again I might be SI-free but I couldn't say for sure.