No it should let you take 48MP photos in good light at 12MP photos in low light using pixel binning this has been reported.Photos from the 48 MP sensor will still be output at 12 MP if pixel binning is used, meaning the photo sizes will be about the same, and I suspect that will be the default setting on these new iPhones.
Just like Apple doesn't set these phones to output RAW or ProRes by default, they won't set them to output 48 MP by default either.