*)There is no legality involved if the marriage is not solemnized. Rather it is betterment for both as they/ either of party has decided not to marry to each other based on mutual differences.There is no illegality involved and therefore no implications. There could be an (unsuccessful) attempt to claim damages. 2)yes in order to harass they can file police complaint,but do not worry so much ,it will be more comfortable then fighting a case when you are married.
Girl and her family may approach police and attempt to file a false police complaint against boy and his family members in order to extract money from them. As such, boy’s family has to be on guard and, if necessary, apply for bail. 4)it is difficult to believe your statement that roka ceremony has taken place and no gifts exchanged .
*)Generally in roka gifts are given to boy and his family .if boy desires to cancel the marriage after roka it is only fair that he pays girl side expenses incurred for roka . similarly cancellation charges if any for booking of banquet hall should be paid by boy side . gifts if any have to be returned )you have not mentioned whether any physical relationship had taken place between boy and girl after roka inorder to harass the boy girl side would definitely try to extract some money by lodging police complaint . please note that if sexual intercourse has taken place after roka girl side would definitely file case under section 376 of IPC for rape