Praise be to Allah.
Your leaving the bank because of what you mentioned of them employing more women without any strict conditions and your agreeing to work for half of your salary, is indicative of goodness and success for you. If a person gives up something for the sake of Allaah, Allaah will compensate him with something better than it, and if a person fears Allaah, He will grant him provision from (sources) he could never imagine. One halaal dirham is better than a hundred dirhams from haraam sources. No body is nourished on haraam things but the Fire is more fitting for it, as the Prophet SAWS (peace and blessings of Allaah be upon him) said.
If the matter is as you describe, that the bank is not abiding by Islamic laws completely, and they only follow sharee’ah when dealing with individuals, but when dealing with companies and the exchequer, they deal in riba, then it is not permissible for you to work in areas that are not abiding by Islamic laws completely, and it is not permissible for you to work in any way that helps and supports riba.
Similarly, it is not permissible to work in a place where men and women mix, because of the serious evils that result from mixing. This has been discussed in the answer to question no. 50398.
What you have mentioned about the environment in which you work now being a bad environment filled with backbiting, hypocrisy and factionalism is something that can be overcome by working hard, offering sincere advice and calling people to goodness.
If it is possible for you to work in the bank far away from riba and mixing, then there is nothing wrong with you going back there, otherwise be patient and seek reward, and have great hope for that which is with Allaah.
We ask Allaah to guide us and you.
And Allaah knows best.