The oldschool 10/10 sundering is most definitely worth something to collectors, yes!
I've seen the 10/10 sundering sword mods get quotes of 50k or more. (I bought a couple once on a big thread based on a screenshot of a spreadsheet list for 5k ea. without anyone outbidding me. Later, when mentioning that, I had a couple major

reactions that, iirc, included things like those go for 50k+.) The sword one, while the most popular,
may be the only one left which can still be produced in the game. I've heard there's some Prophecies (maybe in the Jungle areas) quest reward that still comes with a salvageable 10/10 sundering hilt. I don't know what quest it is, and I have yet to manage to go hunt it up. Anyway, IF that's true, then the 10/10 Sword mods actually do still have some source of new supply.
I've never heard any mention of existing sources for 10/10 sundering mods for bows, axes, or hammers. I've seen more than one "serious" collector seeking them over the years.
Unfortunately, I have no more numbers to offer you regarding price of your bow string. But it's not merch food, not at all!
Cheers & GL!