I will say only about the final out come.
USA will lost it foothold in Asia including Singapore certainly.
NK is only the surface phenomena and triggering factor. The Primary Factor is USA itself rotting weakening and dying off, not just due to Trump. This IS the inevitable outcome and it's superpower status is unable to retain, it allies are all dying and weakening together so the will be NO MORE FOOTHOLD sustained in Asia for USA.
The Secondary Factor is PRC & Russia, not only strengthening and developing rapidly, they are collaborating closely and INCREASINGLY INTOLERANT of US presence and position in Asia. They HAVE exactly the power and strength and resolve to OUST USA together and their SOLID FOUNDATION is way more than Sufficient to reach this goal of ousting USA from Asia & plus Take Over as the next Dominance Superpower. This is an inevitable outcome.
NK is the smallest factor in this game actually, but it CREATED PERFECT Opportunity for Russian & PRC, which Moscow & Beijing are fully taking advantages of.
The part 1 of the net result is South Korea will be eaten by North, by their own strength and with the subtlety hidden assistance of Chinese and Russian. And this outcome is both inevitable and to the advantage of Russian & Chinese, which I will explain later.
The Part 2 is Japan will also lost the so called Protection Umbrella of USA, but unlike Kim Chi South Korea, Pyongyang will not occupy them, but it have no more choice and bow down kneeling before Moscow & Beijing just alike what an obedient dog it had been submitting to USA all these years since it's surrender to USA in WW2. The significant change is that Japs have to serve 2 new bosses instead of 1 USA.
The Part 3 is Singapore will also the so called Protection Umbrella of USA, but completely instable unlike Japan. When Chinese and Russian see their opponent USA lost the power and strength capable of holding oversea bases in Asia (more generally GLOBAL as in even EU & Middle East) by suffering a Global Strategic Defeat, Financial Deprivation, budget cut, military strength lost and humiliation suffered, Washington will be forced to CUT & CLOSE oversea bases almost completely, definitely including Singapore. When Chinese & Russian achieved this stage, they will NOT TAKEOVER bases such as Singapore - contrary to your expectations! Because it is UNNECESSARY. Chinese & Russian does not really need to deploy nor protect nor uphold any ex-USA bases - simply because there is NOT NEED to, as USA is out, there is no other global opponents capable of holding these bases to Choke Hold nor Threaten nor Challenge the dominance of Russian - Chinese alliance at all. They will have all free passage and whatever remains in this world are all insignificant to Choke Hold any Strategic routes to hinder Chinese - Russian interest. If Chinese Russian wanted somewhere to refuel or resupply, Singapore will NEVER be the only port willing to do that, and they have endless choices to pick from - as long as there is no USA to fuck around any more.