He probably can grant you power of attorney, but he would likely have to get his signature notarized at the US Consulate in the country where he is now living. The other matter is whether you complied fully with the terms of the bond; if not, the bond may have been breached and the money forfeited. Aside form checking with the local ICE office, consulting with an experienced immigration attorney may help.
This answer is of a general nature and should not be relied upon as final, nor is it intended as legal advice. A consultation with an experienced attorney is always the best way to go.