Trump will not be a factor in the greater scheme. The Koch brothers may well outlive his tenure. They may not. If they don't, they have heirs. The political climate will swing once more and largess will flow to the Republicans.
After all, they are only the most celebrated Republican donors, not the only ones.
Politicians - and their donors - have short memories and function from interest to interest. The past is the past when it comes to what the donors want and what the politicians promise to deliver. In this political climate, what is most important to conservatives is that Congress stay in the hands of the Republicans, and the Koch brothers will act to see this happens regardless of their retirement status. On top of that, Republican supporters will take food off the table to send money in to their local congressional elections. They hate Democrats that much.
Senators elected today do not leave office for six years. Multiple Republican senators are far more important than one President, no matter how stupid his base is.
My point is that it doesn't matter one bit whether the Koch brother live, die, or take all their money and hoard it in a yurt in Ulaanbaatar with George Soros as a roommate. Ain't no politician gonna suffer long term over Trump. He is simply a blip - an incredibly embarrassing, aggravating and ignorant blip, but a blip who will fade away and be remembered to history as America's worst hour, despite my brother's protestations to the contrary.