The rules actually allow the bereaved spouse to apply for ILR as long as the marriage was still subsisting at the time of the death. See paragraph 287(b)
http://www.ukba.homeoffice.gov.uk/po...ivil_partners/
Obviously you may be able to point to cases whether the HO refused ILR, though you may be thinking of people who were here on a fiancee visa who had not yet married and applied for FLR. In these cases it would not be possible for them to extend their visa.