Dependants hold status derived from the principal's, so their status is affected by the same event. Regulation provides a limited discretionary period after employment ends for several classifications, capped and subject to the remaining validity of status. It is a window for taking action, not a period of continued permission to work.
Derived status ends with the status it derives from
The dependants' position is entirely contingent. A spouse and children admitted in TD status hold that status because the principal holds TN, and if the principal's employment ends the foundation is removed. Regulation does provide a limited period after a cessation of employment for a number of employment-based classifications, capped in length and never extending beyond the validity already granted, and it is discretionary rather than automatic.
Its purpose is to allow a person to arrange a change of status, find a new employer or depart in an orderly way. It is not a grace period in which work may continue, and dependants in TD status may not work at any point. Households should therefore plan the response in advance: what the family would do if a contract were cancelled, whether a child mid-school-year would remain, and whether anyone in the household has an independent basis for staying.
Knowing the answer before it is needed converts a short window into enough time.