The treatment has severely disturbed the swarm and the ones that are not killed will move on to another location within a few hours.
The most common wasp is the paper wasp which hovers in flight and nest above ground. They often nest in or under eaves and under fence capping.
The European wasp is a notifiable pest to the Agricultural Department. They live in large colonies of up to 5000 wasps in an underground nest. You are much more likely to have paper wasps which nest above ground in colonies of around 30 wasps.
No, the wasps do not return to an old nest. You may simply destroy an old nest.