Lack of Touch ID would require Apple to rewrite their Apple Pay agreement, which means that every retailer and every bank would have to agree to the new one. Remember how long it took for some to get on Apple Pay in the first place? It'd be a huge problem for millions of users while we waited for all of them to accept such a change.
I just don't see them completely leaving Touch ID, especially considering they just added it to the MBP. If they were transitioning away from it to a camera-based system, why put in the work to add it to the MBP, only to remove it and have to integrate the new system a year later?
Umm, don't be so sure. Does Apple Watch have Touch ID? No. Does Apple Watch use Apple Pay? Yes. Did Apple need to renegotiate all of their agreements just for the Watch? I doubt it.
Their terms probably states that payments will be authorized with some form of secure authentication process. Apple Watch is authenticated through a passcode, and then left authenticated if skin is detected. Arguably, this is not a very secure form of authentication, as a Watch can be removed with a hand covering the back and remain authenticated.
In fact, did you ever notice the "Pay with passcode" option within Apple Pay? I'm not sure where everyone came up with this theory that Touch ID is central to the whole architecture of Apple Pay, because that's just flat out wrong.