Can Shadow Word: Death kill a Spellbender minion?
Solution 1:
The secret will trigger and the 1/3 will die.
Generally any spell cast on a minion will trigger the secret and affect the 1/3 regardless of whether or not the 1/3 could usually be targeted by that spell. So things like execute (which normally only affects damaged minions) or bestial wrath (which normally only affects beasts) would also affect the 1/3.