Way of the Assassin Quest Broken

Alright, I got 2/3 Assassin Guild Leader Tokens and I saw the third I needed to kill but before I got the chance to approach him, he just walked down into the flats and disappeared under the water, never to return. This is the assassin next to the round building and the astrarium and this was before I drained the water with the dam controls. If anyone knows how to get him to come back from wherever it is he went i would greatly appreciate it.