Nah, they'll just fund your competitor as well, and pit you against each other to see who survives :).

Even if that happens, that's fine. Softbank has no incentive for your business to fail. The company that dies, is more money out of the visionfund.

On the other hand, FB does have an incentive. Sure, they lose that investment, but they gain their own internal company that they own 100% of which has eaten your marketshare.