Just to carify
The STS system is a FCC function, there 2 FCC (A and B), Either FCC will provide STS, if there a single failure (speed trim fail light will illuminate on recall) and as noted continue flight normally.
However to dispatch with this failure, that STS must be deactivated (by pulling the FCC Dc circuit breaker, this will disable the whole FCC) you will now be operating with only 1 FCC.
If the speed trim fail light illuminates automatically, this means both STS functions have failed and the STS system will not work. The pilot will hanble this, after landing dispatch is not allowed, you cannot deactivate both systems if you did there would be no FCC's, therefore you must fix at least 1 of the FCC systems