I was wondering how he ended up and the biography on Wikipedia is unclear on how his life may have improved after publishing his results. He published in 1978 and passed away fifteen years later. Other than a note that he joined The Party in 1991 there is no information on his last years.

I am not sure what to make of the information that is given. Does it imply he was treated poorly, even tortured, until 1991 when he relented?

From the Baike page https://baike.baidu.com/item/%E6%94%AF%E7%A7%89%E5%BD%9D you can see he got a lot of reward during the year 1978-1993, including 院士 (member of CAS) which is almost the highest praise of a scientist. Also he is the leader of many official organizations during those years.

More info at https://baike.baidu.com/item/支秉彝 I'm glad he graduated from the same college as me, Zhejiang University.