The coil may well never fail.  Then again it might.  Get a spark tester from your local parts store and install it in the end of the plug wire, and start it up.  If you get enough KV to fire the tester, the coil is okay.   Most point systems use a 20 KV coil.  HEI is closer to 40 KV.  With aftermarket coils, you just have to go by the coil specs. You can also use a ohm meter and measure across the coil primary contacts, and from the primary to the secondary tower connection.  If it's in specs, you are in good shape.