Jonny,
One option is to go home and prepare for another day. If you want to stay, what are the chances for catching more fish? To offer some possible techniques, we have to know a few things:
1. What were the trout rising to before? A hatch? A spinner fall? Female mayflies returning to lay eggs? Ants being blow off the trees? A combination of things as opportunity feeders wander around an area? other???
2. Were you catching trout on top with a particular fly before they stopped rising? What was it?
3. Have the stream conditions, other than the falling of darkness, changed?
4. ***Can you anticipate their next phase in feeding based on what you have observed?
Night nymphing to possible fish locations does not sound like a fun option. However, night fishing, although it has its own complications, can result in large fish.
Tapper