As far as I can remember there was a backup plan before, which was a WS-20 variant with further increased bypass ratio. For once it was exhibited named as SF-1. I can imagine if they used that design, the progress would be a lot faster and the engine can still be highly reliable, as it is rooted from CFM-56, despite the fuel consumption will be greater than that on other latest engines.
But, as most airlines in China are state run, they can still afford to run such aircraft with less profit if it is really required, say in the situation of US sanctions or so. Remember the entire aviation system in China is not working only for profit, which is different to their western counterparts.
But they finally chose to develop a new one from the ground up following the design concept of LEAP, which means they are even more ambitious. I think they are trying to play a full catch-up in order to finally establish an entire civilian engine supply chain with all required R&D and manufacturing capabilities.