For me Neil -Misti relationship is more like big Brother and sister type one ...he is more like Avni protector for Misti ...her superman ..so even after knowing the truth he won't change ... he will continue to keep her safe ...I even doubt whether his behaviour towards Juhi will change after knowing the truth...after some heavy dialogues he may still keep her at hse .the only ones behaviour which may change after knowing the truth will be shweta..even when she thought Misti can be Neil's child she wanted to send her to Canada ...so after knowing the truth we won't know how she will react ...she herself will drop Juhi and Misti at Vidyut's place