Hi 55 first,
i second that recommendation, your points or the coil went bad
maybe... the actual ignition switch got tired and gave up, not much else in that path
coils can ohm out good but still not work, the insulation goes bad inside and the spark shorts out internally leaving nothing for the spark plugs
The OEM ignition system was designed to survive forgetting the key on, it is normal to anticipate folks will forget the key and that shouldn't break your vehicle.
However the realities of the world and the laws of physics means it can lead to permanent damage as some folks can testify first hand.
Clean points make sufficient contact that there is nearly 0 voltage drop at the points, little to no voltage drop means little to no heat dissipation.
The condenser should never fail from leaving the key on if it goes bad it was already bad and you just didn't know it yet.
The OEM coil and resistor (internal or external) limits the current to a survivable amount, about 3-4 amps and the battery just drains.
The coil is large enough it can dissipate on the order of 30-40 watts all night long as the battery drains, it would be hot to touch but not hot like it gets on a summer drive.
I have left the key on in my trucks and i also recall my mom leaving the key on in the 57 chevy car and we have yet to get burned points, so far they have survived.
but we know from experience it can all go south as in your case
best of luck and let us know what you find
-s
