You wouldn't necessarily lose gas from the faulty sensor, possibly the valve under the sensor is faulty but it would leak when you remove the sensor.
Best bet is to get them to check the A/C pressures before they regas it. Unless they're using an ancient A/C machine they will have to remove all the refrigerant in the process so can advise you if it's lost gas/potentially has a leak. Hopefully they've put some u.v dye in it as the condensers can leak