Will the scrapping of the Eurostar sets, or in due course the 91s, release any useful heritage electronics or mechanics for the 89?
I'd be surprised if they did - I don't think the 89 has much in common with the 91s and has very little in common with the Class 373 Eurostar (AFAIK). There's more of the 89's design and electronics that made its way into the Class 9 Euroshuttle locos and the Class 92s.
Added to that 89001 is a unique prototype, so a fair bit of what's in it is probably one-of-a-kind too.
As per the website, it would appear that spare/new parts they need they're either reconditioning the existing ones, or having bespoke new parts manufactured. After what appears to be a bit of negotiating, Brush (Wabtec) have allowed them access to the original design documents, which I'm sure will be useful too.