Lack of indoor coverage in a specific location is not, of itself, a basis for early-release from a minimum-term contract. WiFi-calling is offered as a mitigation to allow full use of your phone for calls & texts, anywhere that you have a WiFi-connection which I would presume is the case in your workplace.
Each of the 4 networks has varying coverage and good/poor coverage areas for each operator are rarely in the same place.
