1) Boss Dies, A leaves and turns in Soulstone + Tyrael (1x)
2) A rejoins game, B Leaves, A turns in soulstone, B Rejoins, A leaves hits resume and turns in Tyrael quest (2x)
3) A rejoins, B leaves, A turns in Tyrael quest (3x)
4) B resumes game, A joins, B turns in soulstone, A leaves and...