Taiwan is rightly armed against any Chinese invasion....whether Taiwan gets help from outside or not.
Any Chinese invasion will come at a cost....which will be even higher if Taiwan gets outside (US, NATO, Australia etc) help. Now it's up to the Chinese leadership, political and military, to decide whether the cost will be worth the conquest...
We're not living in a age where any country can just roll over another. Given the location of Taiwan to China, it'll be a lot easier for the Chinese to annex Taiwan than for China to annex something much further away from its sphere of influence. Even then, that annexation will come with body bags and heightened international aggression against China, along with other short-term and long-term costs.