Assertion: Initially Drupada protested when he heard that Draupadi will be the common wife of Pandavas, but later he consented.

Reason: Vyasa cursed him that if he would not give his consent to the decision, his empire will vanish.

The Assertion is correct but the Reason is incorrect.

Initially, Drupada protested when he heard that Draupadi will be the common wife of Pandavas. However, the seer Vyasa arrived and told him that the Pandavas were in reality incarnations of Indra, whose wife had been reborn as Draupadi, and they were thus destined for each other. Vyasa added that in another instance a young woman had prayed to Shiva for a husband, and in her enthusiasm, had prayed five times instead of once.  This woman was now reborn as Draupadi, and Shiva had fulfilled her prayers. Convinced by these stories, Drupada consented to the marriage.