You are correct, assuming that the coil is ALLOWED to complete its cycle. If we allow this to happen in an ignition circuit the engine won't run so very well.
In a standard battery coil ignition the primary circuit is completed when the breaker points close. This builds up the electro-magnetic field in the coil, which eventually reaches "saturation", meaning the electro-magnetic field has reached its maximum.
When the breaker points open, this stops current flow through the primary windings, causing the electro-magnetic field to collapse. This "collapsing" causes a voltage to be induced in the secondary windings which, having many more turns of wire than the primary side causes a dramatic increase in voltage (with a corresponding decrease in amperage).
This voltage will rise UP TO THE POINT WHERE THE CURRENT CAN FLOW ACROSS THE GAP(S) of the plug and the rotor/cap area. This is an important detail that is often overlooked/mis-understood. As soon as this "breakthrough" voltage is reached the current flows (sparks) across the gap. If we had a coil of infinite capacity to maintain flow then the voltage would indeed continue to rise up to theoretical maximum but in actuality the voltage drops as the current is pushed through the circuit. This voltage drop is similar to battery voltage dropping when a starter is engaged; if the battery had infinite current ability the voltage would not drop. With a finite supply of energy available the voltage simply must drop.
If we put too large of a gap in the plug then the voltage will continue to build up to the maximum level of the coil's capability but will never reach the breakthrough voltage thus causing a mis-fire.
Remember, voltage is Electro-Motive Force (EMF). It is merely the pressure that pushes the current through. Voltage can exist without current flow (infinite resistance) but current cannot exist (flow) without voltage (EMF) to push it through a resistance.
It is the current (amps, joules) that actually produces the heat which lights the fire, not the voltage. Just think about an arc welder; relatively low voltage but high amperage which melts the metal.
Joe