If you still have the key right now and it is your only key, have some duplicates made: at least 2. One so you can run run home and get a spare key to retrieve the motorcycle, and another so you don't have to run out and get a new key made the same week you lose the first one. You may never need either but, it is cheap insurance against lost keys. Somewhere around $3-5 per key at a hardware store or locksmith shop.

If you have already lost the key there should be a code number on the little silver ring around the ignition switch for a new key. Or you can take the VIN number to the dealer and have a new key made. Still relatively cheap at $8-$15 at the dealership.

The best thing to do is always have at least one spare key. Losing your only key is a huge inconvenience.

But if you lose your only key to a vehicle, check with your local dealer. Many can make or order an additional key from the bike's VIN ( serial number ). A locksmith may be able to make a new key as well without having to replace the lock(s).

I don't know about this... I want to know about this...

Whatever floats your boat. We have no way to answer this with out knowing a lot more about the keys. Was the motorbike key the only one lost ? If yes then that is the only one that has to be replaced, however if you lost other keys along with it then it would be wise to replace them all.