I am so sorry for your loss.  If you have knowlegde of the debt owedto the I and you are the fiduciary of the estate do NOT hang your hat on that Notice to Creditors that you published.  The IRS is a very powerful organization with far reaching pwoers.  You have an obligation to advise creditors of his death and it is very possible that you may be able to negotiate the debt so that the estate is not eaten up by it.  Good luck.