Im in the same boat, I don't think it would work because the adapter is expecting TB on the other end. Yes, I know Displayport rides TB but the Displayport side won't be expecting TB.
There doesn't seem to be a USB-C to mini-DP adapter so it looks like if that doesn't work; then I'll be needing TWO dongles to connect to that display.
I ordered the TB3 to TB2 adapter
anyway simply to use for transferring files from my old mac to my new one when it gets here. Which, I know, is a lot of money to spend to do something that I could've done via ethernet; it'd just take more time. Oh well. But it actually works both ways; and I'm planning to order a TB2 storage array too; so it'll spend the rest of it's days plugged into that. So I'll see if it works! If not, then I get to connect TWO dongles to make a display work that was supposed to 'just work' with my MacBook Pro. ah, progress...