That is not true. If there is no sub, the LFE channel is lost. If that were not so there would be a lot of damaged speakers as the LFE is booted 10 db. Also smaller speakers can not be crossed over.
People may not go for Atmos, but 3.1. 5.1 and 7.1 systems are common. It is very unusual for center channels not to be crossed. I would say at least a center channel is common to center the dialog and help voice discrimination.
So, my advice stands, as not being able to connect to the sub out will lose you sales.
I don't see the issue, as it is such an simple undertaking. I realized this issue in the design of my system twenty years ago. It would be a shadow of what it is without that included in the design. It was not an afterthought and should not have been for you either. Sorry to come down hard about this, but for your excellent design this is a MUST redo.