Unless something very unexpected happens, the probability of China retaking Taiwan in 2020 is basically zero for now. In the next two to three years, the Chinese economy could go through a difficult period and Xi, dealing with the internal difficulties caused by the trade war, will have no time for anything else.
Also, China’s military reform will not be complete by then, and there will still be a considerable gap between Chinese and US military capabilities. Although a takeover battle would be fought in China’s near seas, Xi would have to prevent it from escalating into a full-blown war.
Therefore, there could be no attack on Taiwan unless he was absolutely certain of winning, and it would take time.