I don’t try to predetermine how important to my players an NPC will be. It varies tremendously, both in 25 year long email campaign and my live campaigns.
- Several NPC’s have been taken over by new incoming players as their PC. It can be an easy way to jump in a story. (The BG3 companions would be fun to play!)
- Some NPC’s stay NPC’s but are frequently recurring and of varying importance personally to the PC’s. E.g., a barmaid from Return to the Keep on the Borderlands briefly joined the party and often interacted with the party as they made the Keep their home. A romance developed and a PC married her.
- Some recur but are minor. I don’t think the folks in my current live campaign even noticed they met the same courier twice on different road trips, for instance.