This fear makes no sense, you can use ApplePay without TouchID now by using your PIN:I just hope that if Face ID replaces Touch ID on the iPhone 8, that banks, credit card companies, do not stop supporting Apple Pay, due to security concerns. Hopefully with Apple's strong history of security, this will not be the case with the banks and credit card companies.
https://discussions.apple.com/thread/6994870?start=0&tstart=0
If the financial services are happy with this now why would they stop if the iPhone 8 doesn't have TouchID?, they've demonstrated they don't consider it a requirement for ApplePay.