Rohloff's do hold their value well compared to other cycling components, though there's still a point where the depreciation will be more than the value you consider you've had from it
As long as it's the standard black or silver, you have the most popular spec hub, but it's in what is currently the least fashionable wheel size. The latter might restrict the market or value, as in the 26" market will be smaller, and those wanting another size will have to factor in a wheel build and any reluctance to change sizes (This seems to have become less of a thing over the years, Rohloff still recommend against it, but their dealers seem more relaxed about it than they used to be)
Ebay seems a good arbiter of value, find a similar wheel and see what it fetched, search on completed sales, there ought to be enough of them to get a good idea. I was looking for a secondhand hub a couple of years ago, I didn't see anything sell for less than £500 and those tended to be well used rim brake hubs. Anything that looked decent was fetching £700+, I bid on a couple but in the end they all had some compromise on exactly what I was looking for, so bought new which at the time was £1,030. So basically decent wheels and hubs were 70% of the new hub price.
A few years before that I bought the secondhand hub that is now in my folder, I paid £550 for this when the new hub price was £950. But it'd already been in the unusual 24" wheel size, I knew it's history and it was exactly what I wanted, so I paid more than I would have been prepared to on ebay.
I don't know what SON hubs or wheels fetch, I've never considered a secondhand one. An issue with selling that is people might look at the secondhand price and compare it with the new price of a Shimano or SP.
Ideally you'd be looking for a buyer wanting both hubs and in that wheel size, how long you'd have to wait for such a buyer is a complete unknown, but the value to them is considerably more than to anyone else.
