The rules provided on page 175 of Force & Destiny do state that lightsabers may not be sundered, however, Sunder is a specific effect in the game, and it is to that effect alone that this rule applies. It does not mean to extrapolate it out to invulnerability to other sources of damage. Other means of damaging gear still apply.
Spending Advantage, Triumph, Threat, and Despair in Combat
Opponents of a force-sensitive character using a lightsaber still have the option to disarm or damage the weapon through the use of rolled Advantages and Triumph on their attacks, or as the expression of rolled Despair on the wielder's attacks.
For example, three Advantages or one Triumph can be used to include dropping a melee weapon in the narration of the combat. One Despair can be used to include damaging gear that the character is using in the narration. Two Triumphs can be used to damage the lightsaber of an opponent, likewise two despair can result in damage to the character's own. A single Triumph may also be used for a Critical on the opponent.
The only restriction on damage vs lightsabers is that the Sunder quality cannot be used on them. This models the nature of the blade more than the durability of the hilt. In some specific cases, such as an Extended Hilt or a Double Blade, the group may want to reconsider this rule, if it will increase the enjoyment of combat with lightsaber variations.
Critical Injuries
Critical injuries of various types may also play a roll, from losing actions, through dropping items, to loss of the use of a limb, characteristic decrease, and on to dismemberment.
Enemy Tactics
Of course, the easiest way to deal with a lightsaber is to consider the perspective of the opposition. No one wants to close on one.
The use of ranged attacks makes simple tactical sense, and represents the fear the use of the weapon carries with it.
Even with the ability some characters may earn to defend against, parry and even redirect blaster fire, squads and groups of opponents using ranged attacks and/or grenades are an ongoing concern.
An organization, such as the Empire, once aware of the character and their armament, will respond appropriately as well. This may entail a special unit of commandos, or this might mean the use of specialized equipment - perhaps even equipment modded to provide cortosis armor protection. An Inquisitor is also a possibility.
Alternately, and perhaps more enjoyable for many groups, they might employ spies and hope that the activities of the so-called 'jedi' will serve as bait for other rebellious scum...
On using Cortosis:
In FFG Star Wars, cortosis is an Item Quality representing the manufacture from a rare Outer Rim metal which comes in two varieties. One is an Item Quality for weapons (rare) which causes lightsabers to short out for an unspecified but short time. The other is for Armor. The primary effect of the Quality in either form is to provide resistance damaging Item Qualities commonly held by lightsabers and large blasters: Pierce and Breach for Armor, and Sunder for weapons. This substantially levels the playing field for most lightsaber vs melee weapon combat without needing the rare "short out" capability.
In keeping with the intention of the game design, the GM is the arbiter, in conjunction with group taste, on how long such a short out effect would last. EU source material does not agree.
