Is RCT Required In My Case?

My third molar teeth from the last tooth in the lower jaw bone was turning black. I had got the permanent filling done in this tooth about two years back. I was also experiencing slight pain at times because of this, so we went to consult the dentist. Dentist took an X-ray which showed black cavity in top corner of the tooth and some distance away from the nerve. Inspite of that doctot advised RCT. However, he fiiled the tooth with temporary filling to confirm whether the RCT is really required. A week has past and i experience only slight pain while brushing my teeth. Can anybody please advise me is RCT really required or permanent filling will serve the purpose. Please also let me know if RCT can be delayed by about 4-5 months as presently i'm abroard and here treatment is really expensive. What precautions should i take to avoid RCT for the time being?

Thanks in advance.