As TikTok fights to keep its popular video app available in the US, investors in parent company ByteDance Ltd. are being forced to re-evaluate financial prospects for a business valued at more than $300 billion as recently as late last year.Some of these American shareholders argue that, while a ban will take a near-term toll on their stakes, ByteDance's China business is the real driving force behind the lofty valuation and an eventual payday....