Im working on a project that involves facial expressions, my question is, is it possible to use Watson conversation to guide the conversation based on the facial expression ie: sad, happy, angry. For example if your expression is sad, watson conversation must lead the convo to make you feel better etc..
Yes it is possible - you can make Watson conversation follow any logic which you define in your application (including the scenario with emotions) by means of using context variables.
(see more under: https://console.bluemix.net/docs/services/conversation/develop-app.html#building-a-client-application)
The high level idea is:
More specific implementation details will vary depending on how/when you fetch user emotions.