Hi Benjamin,
MOV's are a strange devices. I don't have the physics or math knowledge to answer this with any real technical lingo. But somebody will surely put me right where I go wrong!
Your comment on "permanently opened (closed circuit)" Can only be one or the other. But I understand what you mean.
As far as I understand, your analogy would depend on whether it's a parallel or series connection.
Also whether the MOV failed 'short' or 'catastrophically'. The former, in parallel would continuously blow fuses. The latter, could allow the circuit to continue working normally until the next 'spike/surge' which then causes real damage to the circuit.
But a series 'short' would work and 'catastrophic' would 'open circuit'. Assuming catastrophic failure to mean complete separation.
But in reality, the MOV is almost always changing it's characteristics due to voltage and temperature variations. Time being another important factor too.
And it's job is to absorb voltage surges and dissipate heat from those surges. Most failures are due to bad design. If a higher rated MOV was used, it wouldn't have failed so quickly.
So your analogy can't really be used unless we use 'automatic gate valves', 'temperature switches', 'diverter valves' and 'expansion vessels'.
I think!!.
So, the MOV has two or three ways to fail. Open circuit, Short circuit and as linear resistance.
To keep it simple for me too, MOV's that have catastrophically failed 'open', can be left in circuit only in a parallel circuit. That being said, you wouldn't know a fault existed after replacing the fuse.
Obviously in a series circuit the opposite is true.
Martin