We'll most likely agree to disagree but Taiwan still holds a very strategic value in the concept of first island chain. Missile barrages still can't knock of defenses that are well protected deep in bunkers, caves, and mountains. My opinion is that time and closer economic integration will eventually bring the two together in a peaceful manner. But that doesn't mean Taiwan should abandon defenses because the very thought of them having a credible defense is sufficient to deter China from making that mistake of using force. If China goes to a level of flat out annihilation via barrage of missiles, it will invoke a response from the world and the US whether they had wanted to or not.
For Taiwan, working on ballistic missiles of their own and even fielding a few SSBNs would be the ideal counter strike that would nullify the thought that simply being able to establish a beach head on Taiwan means all defenses have been neutralized. Because then the PLA generals have to contemplate the cost of counter missile barrages to Chinese cities. Taiwan doesn't need to develop missiles or subs with ranges that have to be world-wide, just far enough so it's not tied down to the island so any Chinese initial strike won't be able to destroy them.
Quite obvious that by the time mainland DOES decide to attack Taiwan, any conventional thoughts about inter-strait relations are already invalid. By that time, any attack methods short of nuclear or targetting civilians would be considered normal.
Taiwan's military can run, but they can't hide. How big is Taiwan; not very. How big are their mountain ranges; even smaller. After the PLA lands, they will find any remaining defences or cave systems due to Taiwan's small size. The missile barrages are to ensure the PLA can land with sea and air superiority, not to ensure that the PLA will not encounter any resistance once landed.
China can overwhelm any of the small countries surrounding it including Mongolia, Thailand, Vietnam, Nepal, Bhutan and Laos and yet it does not because it goes against international convention. Should Taiwan abandon its military, which as of now is already quite light on the balance of power, the mainland would still refrain from attacking Taiwan needlessly. The point here is to "reconciliate" not "dictate", Taiwan needs to WANT to be part of the PRC or in extension, the Chinese nation; forcing them would invite chaos and disunity.
Taiwan with SSBNs is the most destabilising act in East Asia since WW2. I assume you just threw the nuclear non-proliferation act out the window Look at inter-strait relations now, Taiwan hasn't been attacked even though it's quite obvious they will be defeated, the mainland is restraining from upsetting the reconciliation process. With or without Taiwan's military, the mainland would not be "making that mistake of using force". If the mainland does attack Taiwan, it would be because they chose to elect another retard like Ah Bien and went along with his/her separatist views.