1. Are you contending that China would NOT give asylum to North Korean army defectors?
Depends. What can they offer the Chinese? Furthermore, why are we sure that this specific segment of the North Korean military would successfully defect when the North Korean state would make a maximum effort to ensure that the would not? As said as it is, totalitarian states are quite skilled at manipulating human ties to ensure loyalty and obedience.
2. Are you also contending that the Peoples Army would actually operate efficiently and loyally in spite of multiple purges, famines and that 90% of the army has more experience farming rice than conduct real life battle tactics.
This is something of an unknown. KPA military doctrine is based on a melding of Cold War Soviet theory with Chinese light infantry arts, and some homegrown modifications to Korea's particular terrain. There is a focus on massive preemptive strikes, and with heavy dashes of unconventional commando warfare behind enemy lines, while infantry are heavily armed with anti-tank weapons, and expected to deal with enemy armour themselves. For fire support the KPA concentrates on massed artillery barrages, using saturation rather than precision bombardment, and doesn't put a lot of stock in close air support. With pilots getting 15-25 flying hours a year and no advanced combined arms training areas in North Korea, that's probably a good thing - who knows what they'd hit.
All of this force is to be launched at the enemy with speed and surprise, to be part of a never ending attack that will keep the enemy continually on the back foot by its speed and ferocity. Logistically, this would be ferociously demanding, and there's no evidence to suggest whether the DPRK could sustain it. Pre-war expenditure calculations historically tending to be inadequate, and the limited nature of the Northern economy to take up the slack, I rather suspect not. But "One Blow Non-stop Attack!" sure sounds cool as a super-special ultimate combat move!
Although the KPA remains the fourth largest army in the world, its quality, both in relative and absolute terms, is declining. Due to famine and poor health, most KPA soldiers would now fall at the low end of what western militaries would consider fit for service. Although the KPA conducts continual low level modernization, it cannot keep pace with the development of arms in richer countries. It has conducted major modern training exercises since 2001, but these have been relatively modest affairs given the expense involved.
The DPRK is aware of this, and counters their growing material inferiority with an ideology encapsulated by the slogan "One a match for one-hundred!" The basic idea is that the KPA soldier is better prepared physically, politically and mentally for war than his Southern or American counterparts. KPA troops are taught that their "spirit" will overcome any hardship. This kind of thought is historically common among weaker nations attempting to convince themselves that they can take on a vastly more powerful foe due to some intangible benefit they possess and their enemy does not.
It's basically based on rampant self delusion. It didn't work for France when it was called "elan," it lead Japan to disaster when it was the "Banzai spirit," and it certainly won't serve the DPRK any better. However, a note of caution that just because this policy won't be effective does not mean it won't inspire blood lust that will wind up getting a lot of people (both the North Koreans and their enemy's) killed. The Japanese, after all, did manage to inflict significant casualties upon attacking US forces before being inevitably destroyed themselves. Likewise for the French.
It should further be noted that we honestly have very little idea how good the North Koreans actually are. Their doctrine itself seems to be based on wishful thinking ("one a match for one-hundred," and making a virtue out of technological backwardness). Under all that self delusion they might actually be decent soldiers... or years of resource starvation may have taken their toll, and they may be pretty horrible.
So in short, will North Korea fight efficiently? Kinda, maybe. Loyally? Maybe. We just can't know precisely how much the North Koreans have taken the above delusions to heart except by actually fighting them.
In any case, the performance of the entire KPA is not relevant in terms of the use of nuclear weapons. Only that segment entrusted with the DPRKs nuclear arms is the relevant segment and given the importance North Korea has thus far placed on their nuclear program, we can expect that segment to be the most loyal and competent segment of their entire military.
And they certainly have very little reason to defect to us. To start with, we'd have to kill a very large number of them to impose our power like we did with Iraq...
Of course, if the war were started by a crusading America out to "liberate" the North Korean people from the hateful Kim regime, China would see this as another threatening step towards legitimizing the dangerous "Responsibility to Protect" doctrine, but this time on its border in an area of vital interest. It would be quite likely to threaten intervention to get the Americans to back off. And it would be the Americans who would be insane if they persisted