More or less the only group that's going to gain any benefit, at bloody all, from an NK invasion is a mostly uninvolved* third party that wants the involved to be weakened. It's a powerful likelihood that even the NK populous would be in a worse position from it for at-minimum several years out.
In my opinion, that group will possibly be United States of America, provided that they don't use military force on the ground in Korea. The war or its aftermath will devastate the South Korean economy and create much instability on borders of their geopolitical enemies (China and Russia). It's a perfect situation for America, no pesky Samsung phones will steal money from Apple anymore and China will have to deal with the whole mess instead of America.
That's really not a viable approach, at least for the majority of international thinkers in the U.S. South Korea (and Japan) are important U.S. allies precisely because they help counterbalance China, and a not-insignificant element of that is a holdover of old Cold War policy. The last thing the U.S. government wants is for the Koreas to fight, the U.S. to stay uninvolved, and China to step in and "deal with the whole mess". Intervention on the behalf of South Korea would almost certainly be a domestic disaster for the U.S. government if it ran longer than a year and saw U.S. ground forces committed, but South (or a unified) Korea falling into China's sphere of influence would be an infinitely worse international disaster for the U.S. government. It's worrying enough for these people that Japan's largest trade partner is now (IIRC, it happened recently) China, never mind the possibility of an alliance between them and South/Reunified Korea. Hell, war between the Koreas with the U.S. intentionally avoiding participation would be a massive coup for China; they have the opportunity to upstage the U.S., tighten bonds with South Korea, and deal with the ongoing disaster magnet on their border. Same sort of idea as with Chinese investment and aid in Africa, except a high-profile moment rather than long-term systematic development.
That aside, it's a rather simplistic view of the economic angle; South Korea is a supplier of relatively cheap consumer goods, predominantly electronics. Something like a war with the DPRK would obviously trash that, which in turn means price spikes in the U.S.; we're firmly post-industrial, and even the high-tech sector of production is still relatively insignificant compared to the service sector (or foreign imports). Drastic reduction in the volume of goods imported from
any of our major trading partners would be painful for the U.S.; certainly U.S.
businesses competing with those imports would benefit, but that doesn't equate to it being good for the U.S. government or population. Same deal as implementing protectionist trade policies: it's good for the firms that face reduced competition, bad for everyone else (except for developing states that need to protect fledgling industry from being overrun by cheap foreign imports--including, coincidentally, South Korea a few decades ago).
Basically, the U.S. government has nothing to gain in the economic or international political realms by avoiding intervening in a Korean war. Literally the best outcome (from the perspective of the U.S. government) of such a situation would be a brief, inconclusive war between the Koreas, with no external intervention, which does not change the status quo. To put it briefly, that is... unlikely.