If the wife hates her husband in such a way that she does not fulfill her marital religious obligations with her husband or she threatens him in a serious way to stop fulfilling such duties, then it is permissible to divorce her by way of khula, by her paying him in exchange for him giving her the divorce. In this case, the husband cannot return to the marital relations during the waiting period (the iddah). In other cases, the divorce may not be by khula, like when they both agree to drop the husband’s financial obligations for the wife in exchange for him divorcing her. The divorce in this case is conventional, i.e. the man has the right to return to the marital relation during the waiting period.
The reason behind the waiting period is not necessarily identifying the father if the woman is pregnant. If this was the reason, then it would have been sufficient for Almighty Allah the Divine Legislator to consider one menstrual cycle as a waiting period and not any longer duration. Almighty Allah knows the actual reason behind such legislation. Therefore, the iddah must be observed even if contraception was used.
If it was proven to you that one of the living Marjas is more knowledgeable than the deceased Marja that you used to follow, then it is obligatory on you to switch to the living Marja. If this is not proven to you and you used to follow a religious scholar that satisfied the characteristics of the Marja then you should continue following him.