Yes, the coaster will open as "stand alone" attraction when it's completed between august and October 2019. (e.g.) The SLC was opened on 12th September.
And it's only the RMC. The themed area with the dark ride and kiddy attractions will open April 2020.
Considering the dual launcher is opening in 2020 I guess they had to spread their investments out a bit somehow? Either way I doubt this would change many plans as the ride will still be open in 2020 (unless some extraordinary disaster happens) and you'll have the bonus of a shiny new vekoma!
Has the park yet issued any formal statements about Zadra? We've got a half-finished news piece for the CF front page for weeks now, just waiting for something official to cite that's not a third-party video taken at a closed event.