You might hear that if your T doesn't go away in 6 months, it is permanent. That is a myth. "Six months" is just a time interval that insurance companies use to classify a condition as being chronic. It has no medical basis.
Multiple sources seem to use "2 years" as their rule of thumb. See, for example
https://www.ncrar.research.va.gov/Education/Documents/TinnitusDocuments/01_HenryPTM-HB_1-10.pdf
"A general guideline is that tinnitus of at least 12 months duration has a high likelihood of being a permanent condition (Dobie, 2004b). However, it also has been suggested that a person must have experienced tinnitus for at least two years before it should be considered permanent (Vernon, 1996)."
Link to Dobie 2004:
https://books.google.ca/books?hl=en...AfBTNxz1AY#v=onepage&q=dobie tinnitus&f=false
If your T keeps fading but is still audible 2 years after onset, there is no reason to think that it will stop fading after 2 years.
It will most likely continue fading. A number of members of this forum had stated that the first time they got tinnitus, they eventually got to hear silence after 12-18 months. This is evidence contradicting the statement above from that Dobbie 2004 study.