In example 1, The principle server goes down and you have no witness so the mirrored databases remain in a restoring state. They can be put online if you need to access them but if you do that you would have to recreate the mirroring when the principle server comes back up. If the principle server comes up and you haven't put the databases online then mirroring will resync and carry on.
In example 2, The mirror server goes down. The principle server carries on but the transaction log will start to fill. If the mirror server comes up then mirroring will resume and carry on.