76. On the death or discharge of one of several co-trustees, the trust survives and the trust-property passes to the others, unless the instrument of trust expressly declares otherwise.CHAPTER VIIIOF THE EXTINCTION OF TRUSTS 77. A trust is extinguished,-(a) when its purpose is completely fulfilled; or (b) when its purpose becomes unlawful; or(c) when the fulfilment of its purpose becomes impossible by destruction of the trust-property or otherwise; or(d) when the trust, being revocable, is expressly, revoked. 78. A trust created by will may be revoked at the pleasure of the testator. A trust otherwise created can be revoked only-(a) where all the beneficiaries are competent to contract - by their consent;(b) where the trust has been declared by a non-testamentary instrument or by word of mouth - in exercise of a power of revocation expressly reserved to the author of the trust; or(c) where the trust is for the payment of the debts of the author of the trust, and hgas not been communicated to the creditors - at the pleasure of the author of the trust.Illustration A conveys property to B in trust to sell the same and pay out of the proceeds the claims of A's creditors. A reserves no power of revocation. If no communication has been made to the creditors, A may revoke the trust. But if the creditors are parties to the arrangement, the trust cannot be revoked without their consent. 79. No trust can be revoked by the author of the trust so as to defeat or prejudice what the trustees may have duly done in execution of the trust.