Some can, some can't. Larger air-transport category aircraft have a maximum landing weight limitation. If enough passengers, baggage and fuel are aboard, the plane could be over the limit. If the plane could not complete the trip, perhaps because of weather, it would have to circle around, burning fuel, until the weight was low enough. In an emergency, the plane would dump fuel overboard to lower the weight. This situation generally happens on long flights where the plane is in the air many hours and thus requires a large fuel load, such as on trans-oceanic flights The limitation is not whether the tank is full or not, but total weight. The same aircraft with full fuel and no passengers might be legal to land with no problems. Smaller aircraft actually have the opposite problem. If they are overweight, there is not enough power to take off. If they are light enough to take off, they are light enough to land. So the precice answer to your question depends on the model of aircraft and the additional weight of passengers and baggage.
The fuel in the plane's tank was sufficient, so the plane could land safely.
Specify the type of plane; it varies.
I am pretty sure they have a reserve fuel tank.
Allmost allways add it to a full tank.
It depends on the plane. Some private/borderline ultralight planes only have a range of 100 miles or less, while commercial planes can fly across the Atlantic.
Defective fuel sending unit.
It shouldn't. You should probably replace your fuel filter (which is inside the fuel tank).
The tank should be drained before removal. The fuel must be drained into an approved container.
7/8 full
If you are sure the tank is empty and the fuel gauge is reading half full, then there is something wrong with your fuel level sending unit located inside the tank on the driver's side of the vehicle. Probably the variable resistor.
In most cases the fuel gauge sending unit in the fuel tank has failed.
That can depend on the type of plane and the age of the plane, plus how much gas is left in the fuel tank.