The first signs you may have issues with your exhaust could be scraping on the ground, rattling or banging noises.
However, not all exhaust issues end in needing a replacement if the system is in good condition. Most common exhaust issue is broken hangers, causing stress on the system. It's a small fix to re-weld the bracket back on.
Worst case scenario, if the exhaust system is rusted then a replacement would be needed. Most parts can be available same day at Sandford Motors Service Centre.