He didn't know how long the battle would continue, or who would emerge victorious, but he did know that if Master Deivon fell too quickly, it was game over. Martial Masters operated in a different dimension of speed and cognition.
Master Deivon had traveled the distance between the Virodha Theocracy and the Seonmun town in less than half a day, a distance that Rui would take weeks to travel.
That meant that he needed Master Deivon to stall Master Uma for quite some time if he wanted to have any chance of getting away. He had already known that Martial Masters possessed sensory ability that was extremely powerful. Their senses were to Martial Seniors what the latter's were to Martial Squires. They were two orders of magnitude higher than Rui, at bare minimum.
The combination of their speed and their senses meant that running away and hiding from them was essentially impossible for Martial Squires unless they had an enormous headstart.