I think this shooter could have blended in with the chaotic crowd and escaped, "IF", the fire alarm hadn't gone off, other clients hadn't heard the gunshots, and the security guard hadn't gotten there so quickly. The stairwell was right outside the shooter's door. He could have taken a handgun, and left if he had more time to do so. As it was, he didn't know if the security guard survived, didn't know if there were LE in the stairwell, etc. The response was so quick, the shooter didn't have time to escape.
But, without knowing those things were going to happen, his plan may have been to walk out of his room and blend in. Afterall, no one knew who the shooter was, therefore staff nor LE would have been alerted to him in the crowd.