I'm not familiar with this engine but am unable to understand how the fuse "entered" the engine unless a main cover had been removed?
If it's definitely in the engine, you may get away with it but if it gets caught between gears, the plastic casing will break in to many pieces...... It could also get caught in the gear selector mechanism.
I dropped a shim down the camchain tunnel of my GSX-R1100 a few years ago. Drained the oil & removed the sump & strainer without finding it. I ran the bike for 4,000 miles until the next oil change, expecting to find it in the oil but could not. I gave up finding it without an engine strip only to find it stuck to the magnetic drain plug with just a few scratches on it.