Based on Ubi's willingness to keep working with Epic's store actually.
There is no downside for Ubisoft here. None. They take the fat bag of money, the preorders stay up on Steam until release for the people that want it on Steam. They then sell it on their own store as well, which is for the people turned off by Epic. The sales results are literally irrelevant, and you can even bet that if anything was selling well on the Epic Store then Tim would be thumping his chest about numbers.
Hypothetically Ubisoft games could sell 10 copies each on Epic while honoring Steam preorders and continuing to sell on their own store, and Ubisoft would continue to take Epic's money up front. Ubi can't lose here and it's got nothing to do with how a title sells on Epic.