Should TikTok go away, "this equates to billions of dollars potentially up in the air for competitors to seize," Sensor Tower told CNBC in an email. Emarketer estimates that Meta and YouTube could grab about half of the reallocated dollars should a ban go into effect.

That type of market shift has taken place elsewhere. India banned TikTok in June 2020, when the app had about 150 million monthly users in the country. A year later, Instagram's monthly active users in India had increased by 20% while YouTube's had gone up 11% year-over-year, according to Sensor Tower estimates.

"That's when we saw the biggest jump in Reels utilization ever," said Meghana Dhar, a former Instagram executive who was at the company at the time of the India ban. "Should TikTok get banned and creators have to scramble, between YouTube Shorts and Instagram, a lot of creators are already hedging their bets."