That is a theoretical scenario. Coming up with Jet engine by itself in China "soon" will be tough. The ARJ-21 design itself was built from DC-9/MD-8X design and tooling lent to China by MDD in the 90's, and new Russian-designed supercritical wing and engines were added. C919 design was from Chinese local designers.Previously Chinese airliners and helicopters were powered by Pratt & Whitney turboprop and turboshaft engines.
But Canada has to sfop supplying these engines due to export objection by USA over its technologies to stop China from using them in their military.
I see a similarities in the ban of semiconductors to Huawei and SMIC today.
Yes. It will staggered China for awhile and after that, USA has completely lost control.
Soon it will be an all Made in China own IPR or US technology free suite.
India Tejas which use the GE-404 turbofan face a similar risks of embargo.
However developing aero engines and turbines is not simple effort. It took the US over a hundred years to get to the current stage from zero (hijacked Nazi aerospace/jet engine talent and British Whittle turbojet licensing helped after WWII).
It is my estimate that it will take China another ten years at the very least, and more likely fifteen/twenty years even if engine help comes from Russian/Ukrainian engine designers like Ivchenko and Motor Sich. Russian engines are not even 70% as fuel efficient as US/French/British engines are, even today, despite their claims to the contrary. And forget about FAA approving the flight regimes of these Chinese jets.
Unlike ten years ago, the Trump administration is currently very active in blocking technology sales to China (this is his election platform).
So I see the ARJ-21 and C919 projects being delayed by at least fifteen years, not to even talk about C929 (787 competitor).
Sad but this is fact. Homegrown passenger jet engines in China will be a long shot.