By looking at their Iphone lineup, i can say that they will add colored Airs instead. Iphone has every price segment covered from SE2, XR, 11 to 12. They are trying to catch every dollar from every consumer's group.IMO, due to how capable the MBA is I don't see Apple keeping the 13" MBP around.
I highly doubt that they would allow for a gap between Air($1000) and Macbook Pro 13($1800) and MBP 16($2400). Most likely the low-end MBP 13 will stick around as a lagged version of the higher Pro 13. Well they always did this and it worked most of the time.