A nuclear deployment in 1989 would come at a very strange time for Taiwan, if political developments still largely occur as OTL. Over in the Mainland, Tiananmen Square would occur in the same year, and the Wild Lily movement is a year away. Lee Teng-hui would be still relatively fresh in office, with the Mainland faction in the KMT still plotting to remove him. This bloc included Chief of the General Staff Hau Pei-tsun and Soong Mei-ling, among others, who were key figures in the decision to carry out nuclear proliferation, so it would not be amiss to suggest they could use the weapons as leverage against Lee in some capacity. On the other hand, it would not be unexpected if the student movement were to include de-nuclearisation as part of its program. Lee himself didn't seem inherently opposed to nuclear weapons development, so I don't see a reason he would pull the plug without substantial internal or external pressure.