Fuel will drain past the pump. If you have a stuck float needle, fuel will drain into the combustion chamber and likely hydro lock the engine. There have been some ruined engines because of this.
i had this happen once but was very lucky, the cylinder with the raw fuel happened to have the piston at the top of its travel. When I hit the starter it was locked rather than starting to turn over and slamming that piston into uncompressable fuel and busting the piston,, rod and or block. I took the spark plugs out,and turned over resulting in fuel spraying all over. The crankcase usually fills with fuel too.
Now I absolutely never shut my bike off without turning off the petcock. I don’t even think of it as it is now such a habit. The reverse when starting - turn the fuel and pull the choke out