Can chronic autoimmune urticaria go into remission? Will taking levothyroxine for thyroid help stop the hives without taking antihistamines?

Yes. The average duration of chronic hives lasts for 5-6 years and thus remission is indeed possible. As for thyroid, I have only had one patient with thyroid antibodies benefited from thyroid replacement out of the many hundreds I have seen over the years. Usually antihistamine would be needed. Studies so far with thyroid replacement have mostly been negative.