Well, it had a sort-of ending. As in, the gameplay ceased. There was no message like spending three dozen tries to beat the final boss on Karnov on the NES just to see "Congraturation!" or something equally goofy. Riddle of the Sphinx did end, it just went to the color-shifting like most Atari games do when you'd lose all your lives.

Texas Instruments offered Imagic the TI-99/4A. When TI decided to discontinue their home computer, they looked around for some other company to pick up the ball and run with it, and they really wanted Imagic to take it over. But they weren't doing all that well after the 1983 game crash, and they passed. i wonder what could have been accomplished if the TI-99/4A could have survived and become Imagic's main focus.