Well, it looks like Erudin has a respawn time of 24 minutes, so it might have been worth it to just chill, kill some mobs, explore, or log out for 24 minutes.
https://wiki.project1999.com/Erudin
And yes, there is no exp nor loot from killing merchants on P99 anymore.
One thing that's always worth doing is communicating. You can ask the person killing XYZ how long they'll be doing it for, or if they can leave a mob alone so you can buy from it, or do a quest turn-in to it, before they resume killing.