If I have a spine fusion surgery using metal screws and rods, will they ever need to be removed?

Usually Not. Following successful spine fusion, the instrumentation typically remains. Conditions such as a deep infection, nonhealing fusion, and on rare occasion, painful/prominent instrumentation may be treated by removal of the instrumentation.
Usually not. The instrumentation does not usually need to be removed.
Maybe. No definitive answer can be given to you at this time. If the hardware is not causing you pain or limiting your function there is probably no reason to remove it at this time.