Not all - some.
XA / XE / XF are up for sale. XA has been a "christmas tree" for the rest of the fleet for some time now anyway.
IZ / XB / XG will continue to operate.
This has come about as much of the royal mail flying that used to be operated by the F27 fleet is now on 737QC aircraft. Therefore no additional replacements are required.
Hope this helps.