Of course, Roy had to run. He wasn't stupid. He could fight Sargeras's clone, but he would really die fighting Sargeras's true body.
Therefore, after giving Sargeras a big blow and leaving a deep impression on him, Roy achieved his goal, boarded the Void Seeker, and fled into the universe.
After Sargeras reacted, he was so angry that he was about to explode. Not only did this cunning demon Osiris steal the authority of the titans' planetary shield, but he even caused him to fight on this planet and directly destroy half of it. Now that he had taken an advantage, he wanted to leave. How could there be such a good thing?!
In his rage, Sargeras chased after Roy without even thinking.