Taiwan is similar to Ukraine in the split of state recognition, but quite different in international political status. Russia invaded Crimea with the excuse of protecting their citizens living abroad. They are welcomed by Crimeans who favor Russia. This is almost identical to people in Taiwan who favor unification with China.
However, Taiwan and Ukraine are not the same. First, Ukraine is a member country of the UN and Taiwan is not. Second, if there were riots or societal turbulence in Taiwan, China could not easily troop in right away, regardless of its 2005 antisecession law, which does not have any legal basis under international law. It would directly challenge the US’ Taiwan Relations Act, authorized by the San Francisco Peace Treaty.