Deactivated field with the help icon

Logically speaking, since the help text for that field does not offer any value to the user when the field is disabled, it should be fine to disable the icon along with the field.

If, on the other hand, the help text contained information that helped the user understand why the field was disabled or helped him to enable it, then, logically, he would have to leave the icon enabled.

I understand that your particular situation falls into the first scenario instead of the second, but I wanted to make it clear to anyone who reads and may have a different situation.