So is it possible Agnes is still alive?
The body of the drowned woman definitely had longer hair and both William and Cheesman commented on "her beautiful hair" not knowing ( as Sugar does )that she had cut it off before leaving the house. Sugar appears to register surprise when Cheesman mentions Agnes's hair, so possibly she realizes Agnes was not the woman found on the beach. At the end it looks to me like Sugar and Sophie are taking the same route Agnes did, possibly in search of her?