Can Drawmij's instant summons be dispelled without access to the sapphire?

Question

The spell Drawmij's instant summons is cast on both a sapphire (the material component of the spell) and an object (the target of the spell) that is to be summoned by crushing the sapphire.

Normally, I would expect that casting dispel magic on the target object would end the spell. However, the last line of the spell states:

Dispel magic or a similar effect successfully applied to the sapphire ends this spell's effect.

Is this adding an additional way to dispel the spell, or is it specifying the only way to dispel it? In other words, can I dispel the spell without accessing the sapphire, or do I need to target the sapphire in order to dispel the spell?

Answer 1

Yes, you can still use Dispel Magic on the target object

Instant Summons has a Range/Area parameter of "touch", and states:

You touch an object weighing 10 pounds or less whose longest dimension is 6 feet or less. The spell leaves an invisible mark on its surface...

By any sensible interpretation of the rules, the object is the target of the spell, and is the subject of the permanent magical effect that the spell creates (until discharged by crushing the sapphire). Dispel Magic can dispel this spell effect upon the target object as usual - it's clearly a spell affecting the object, and there's no explicit restriction given that it can't.

Instant Summons is just unusual in that it also affects the material component used to cast it without immediately consuming it. The extra note in the spell's description essentially clarifies that the spell also affects the sapphire despite the fact that it is not strictly the target, and so Dispel Magic works on either end of the link created.