"instead of executing" is correct and usable in written English.
You can use it when you want to describe or compare two different actions to emphasize one choice over the other. Example: "He decided to pardon the prisoner instead of executing them."
Instead of executing her outright they left her to die.
"Countries need to look at ways to rehabilitate prisoners instead of executing them," he said.
But instead of executing that arrangement as the trial began the next day, the judge presiding over the case adjourned until late April.
Note that Jemmy Pitts's cut of the twelve lords shows them pole vaulting down a hill, instead of executing grand jetés,which is how they are frequently portrayed.
Often, instead of executing his vanquished opponents, the Emperor would marry one of their daughters and give his defeated father-in-law a job: better a new family member than a rotting corpse.
Instead of executing calligraphy on landscape scrolls like the painter-poets of old, he executes it in the landscape itself, at night, writing in the air with a flashlight in front of a camera set on a long exposure.
In his letter, Mandela recounted how nine men had been condemned to death for treason by Queen Victoria, but after worldwide protests they were banished instead of executed.
Either because the emperor felt him too valuable a man to lose or because Sima Qian himself requested a reprieve so that he could complete his history, he was castrated instead of executed.
And Justice Sonia Sotomayor protested the court's decision not to accept a challenge to Alabama's death penalty process, one of the few in the country where a judge may overrule a jury's recommendation that the convicted be given life in prison without parole instead of executed.
But he adds that if she had merely been imprisoned instead of executed "it's reasonable to surmise that nobody today would really recognise her much, certainly not in England; the Belgians might".
