If someone has an LP in a gauge and forgets to remove it, nothing will happen in the short-term. However, if the LP is left in the gauge for an extended period of time, it can cause damage to the gauge over time due to corrosion and buildup of pressure, which can lead to inaccurate readings or even malfunctioning of the gauge. Additionally, if the LP is not removed, it can cause the gauge to become blocked or restricted, which can lead to further damage and inaccurate readings. Therefore, it is important to remember to remove the LP from the gauge as soon as it is no longer needed.