If a nation has the will to sink them yes. A small craft approaching a docked Navy ship refueling in Yemen was also visible and it's exact location known. It's not so much a sub but what any sub has onboard in missile capabilities. I doubt once missiles are launched toward China's intended targets that China could care less if the Sub and crew survives. Any sub in their hands is dangerous in that respect.
It’s good enough that they know we can take them out preemptively.