The dissident’s lone regret after his 200-mile escape across the Yellow Sea was not taking night vision goggles.

Nearing the end of his jet ski journey out of China last summer, Kwon Pyong peered through the darkness off the South Korean coast. As he approached the shore, sea gulls appeared to bob as if floating. He steered forward, then ran aground: The birds were sitting on mud.

“I had everything — sunscreen, backup batteries, a knife to cut buoy lines,” he recalled in an interview. He was prepared to signal his location with a laser pen if he became stranded and to burn his notes with a lighter if he were captured. He also had a visa to enter South Korea, and had intended to arrive at a port of entry, he said, not strand himself on a mud flat.

It wasn’t enough.

Mr. Kwon, 36 and an ethnic Korean, had mocked China’s powerful leader and criticized how the ruling Communist Party was persecuting hundreds of pro-democracy activists at home and abroad. In response, he said, he faced an exit ban and years of detention, prison and surveillance.

But fleeing to South Korea did not offer the relief he expected. He was still hounded by the Chinese state, he said, and spent time in detention. Even after he was released, he was in legal limbo: neither wanted nor allowed to leave.