It is not absolutly certain but the creators at black isle have said that they are planning on BG3 but it will not follow the child of bhaal saga. They have said it will most likely be placed in a major city again such as Waterdeep. So keep your hopes up they are going to continue the BG series
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"I was born of darkness. My fathers eyes closed before mine opened. I am not of this world or the other, and I have the right to be what I am..."