His fight with Obi-Wan resulted in him letting him go. The entire place was practically in flames and chaos, stormtroopers were shooting at Empire's enemies, all order had collapsed and there were gunshots everywhere. Vader stood by the fire, which was quite strong, and looked into the space where Obi-Wan was before running away, in time avoiding the fire with his gloved hand, a bit covering his mask as the fire got bigger, feeling anger and hate towards Obi-Wan.