The "source of income" doesn't jump ship, because their assets are not so easily moved. The owners can flee, in which case their assets are nationalised. Factories, raw materials, technologies, specialist staff and supply chains do not and indeed, cannot flee.

Unless a Socialist takeover happens overnight, any owner could still plan ahead and sell off certain assets or even begin the relocation process. As for Specialist staff, if they're no longer being paid because the boss is no longer there, what reason do they have to stay either? Brain drain is a real phenomenon since a lot of people value work and having money over not starving.

This is a ridiculous position to take because an authoritarian regime with the necessarily will can maintain its hold on a country indefinitely with or without "rebuilding". North Korea is a perfect example of this.

That's not a great example. North Korea depended heavily on the USSR for support, and when they collapsed, they suffered a devastating famine. It also put the country on international food assistance (to which admittedly, the USA politicized and withheld certain food imports if the North Koreans didn't act a certain way).

https://en.wikipedia.org/wiki/North_Korean_famine

In the 1980s, the Soviet Union was embarking on political and economic reform. It began demanding payment from North Korea for past and current aid – amounts North Korea could not repay. By 1991, the Soviet Union dissolved, ending all aid and trade concessions, such as cheap oil.[7] Without Soviet aid, the flow of imports to the North Korean agricultural sector ended, and the government proved too inflexible to respond.[13] Energy imports fell by 75%.[14] The economy went into a downward spiral, with imports and exports falling in tandem. Flooded coal mines required electricity to operate pumps, and the shortage of coal worsened the shortage of electricity. Agriculture reliant on electrically-powered irrigation systems, artificial fertilizers and pesticides was hit particularly hard by the economic collapse.[15][16]

North Korea's status in the world today is also based on being extremely impoverished. So you could argue Germany would still exist, but then Hitler's Germany would resemble the GDR or something less impressive.

The reason it is not comparable is because there is a massive chasm between industrial magnates and small time private farmers. The USSR did not even necessarily need to crack down on the kulaks, but pursuing its political agenda would have been completely impossible without smashing domestic industrial capitalism. I am not even sure where we are going with this here. Your point was that the German capitalists did not have to submit to the NSDAP and therefore we can consider their donations to be voluntary rather than compelled, but the kulak example you gave provides ample demonstration that the state can obliterate private business on a whim and that these donations were basically forcibly extracted from the capitalists.

It's exactly this, but it's also hindsight because the conditions were perfect where the Industrialists stayed and had no disagreements with the government. We don't have other examples to compare this to where such talks might have broken down and Hitler would have had to try something else. Maybe he could have even gone down the violent route and seize their jobs by force, but there's no telling if such hasty nationalization could have also ended in failure.