The more I think of this, the more I feel this is a bad idea. It's true that we're unlikely to receive this sort of money for Fabinho again, but it's also true I think that we're not going to be able to replace him.
Firstly, I think you need to appreciate the significant gap in importance between Henderson and Fabinho. Prime Henderson was a good player, but statistically very replaceable. Prime Fabinho was a top 3 DM in Europe - that's a rare and elite talent, who isn't easily replaced. Add to that the fact that Henderson is 33, and Fabinho is 30, it is clear whose loss we'll feel more.
I think it is probably right to say that the days of Fabinho playing single pivot are over, but it'd be stupid to ignore the importance of his positioning, defensive coverage as a 6 in the double pivot. He still reads and understands the game at a very high level, and that's simply not available in the market readily. At any given point, there are rarely more than 5-6 elite DMs in the world. Fabinho was one of them, and still offers stability to the spine of Alisson-VVD-Fabinho. I simply don't think we win anything without that spine.
The calibre of player we'd need to replace Fabinho simply won't be available to us - I'm talking Caicedo and Tchouameni. What are the odds we sign them?
It's good to start thinking about transitioning to a new era, but abandoning the idea of actually winning anything quickly isn't a smart idea. Klopp is here for just 3 more seasons. I don't want those years to be like from 2015-2018 where we won nothing. The likes of Lavia or Bajcetic are simply too young, and won't be any better than the likes of Can or Joe Allen we had at that time. Very few teams in PL history have won anything without a great GK-CB-DM axis.