Question: what happens when you beat 100 team rocket grunts?
Answer: You can choose to keep your Pokemon as-is if you wish! Hero Badges in this event include a Team Rocket “Defeat Team GO Rocket Grunts badge at 10, 100, and 1000. You get +1 ball per tier during the Rocket Encounter event. There's also a Purifier Badge that'll give you reward at 5, 50, and 500.