Roy had imprisoned Tyrael's soul in the crystal. Unless Tyrael's soul power could surpass Roy's, he wouldn't be able to break out in a short time.
Imprisoning Tyrael was equivalent to killing him. For a long time, he would no longer be able to interfere with the human world of Sanctuary.
All Roy had to do was wait. The matter of Tyrael's disappearance needed time to ferment, and the relationship between the nephalem and angels would not deteriorate immediately. In order for it to reach Roy's ideal state, he needed enough patience.
Of course, waiting didn't mean that Roy would do nothing. In fact, after considering the subsequent developments after Tyrael's disappearance, he felt that he needed an army, a massive demon army, in order to deal with the possible attack from the High Heavens.
