What happen to the irrevocable trust after the grantos death?

You need to review the document that created the trust. A trust should contain all the provisions necessary to the management of the trust property by the trustee. It should recite all the powers of the trustee and what should happen to the trust property at the termination of the trust.

Title to trust property stands in the name of the trustee who holds title in the name of the trust. The type of trust you refer to usually has detailed instructions as to how the trust property should be distributed upon the death of the grantor and how that property should be transferred by the trustee.