This neuroplasticity occus at a number of levels. At the lowest level, as we've seen, it can involve undamaged axons sprouting new connections to drive the neurons which have lost their input due to the damage. At a higher level, it can involve activating different pathways to accomplish the same funtion in a slightly different way. The reason this all works, is that our central nervous ststem is designed with a lot of redundancy- pathways that are present, but not really needed for our normal functioning. These pathways are then available to take over for the function of our normal pathways when these are damaged.
Redundancy is the heart of neuroplasticity.
Another point is that the neuroplasticity we have available is very much a function of age. In infants and children, there is a large amount of neuroplasticity in the system, because this is also used in the normal development of the nervous system. So a stroke in a young child can often have relatively good recovery. As we get older, neuroplasticity is less and less available, and so recovery takes loger, and is not as complete.