Complete suspension of service to China and significantly reduced demand to the rest of Asia is today's reality, feeing up a large amount of capacity at zero notice. It's not enough time to schedule maintenance, repainting or even to rotate in larger planes on other routes (and it's a quiet time of year anyway). But China will either spring back quickly and, with it, the need to travel there, or the world as a whole has bigger problems. The global supply chain relies on China for so much product - it the supply chain re-opens, global companies need to nurture it so much of the travel is not optional. If it's safe to go, people will go: if it's not safe to go, the supply chain starts faltering (it's closed now, and shortages will hit sporadically in the next few months).
So, in reality, there's little UA can do in the short term but, in the medium term, there's little more than tinkering that will be required, or we have a global crash, which will have much more dire consequences all round.