Gonzalo's death on 26 June appears in the necrology of the Sobrarbean monastery of San Victorián, but the year is not recorded and has been the subject of much debate. The early modern historian Jerónimo Zurita incorrectly placed it in 1035. José de Moret suggested 1042 or 1043. A late source, the Chronicle of San Juan de la Peña, places it in 1037, but there is charter of disputed authenticity dated September 1039 that is confirmed by Gonzalo.[6] As Ramiro confirmed the rights of Bishops of Urgell in Ribagorza in September 1040, it would appear that Gonzalo was dead by then. Pérez de Urbel thus places it between December 1039 and September 1040 and casts doubt on the dates of several documents mentioning Gonzalo after 1040 (a donation of Blasquita from 1041, a charter of Ramiro's from 1042, and a donation of Ramiro to Atón Garcés in 1043). Accepting these, Ubieto Arteta places Gonzalo's assassination in 1046. Nelson gives reason to believe that it was 1043.[7]
The Chronicle of San Juan de la Peña reports that Gonzalo was assassinated by one of his own knights, Ramonat de Uasconya,[8] who threw him from the bridge over the river Esera at Montclús, near Lascorz.[9] He was interred in the monastery of San Victorián.[10] On his death, García awarded his counties to Ramiro.
Gonzalo left no heirs and his short reign was soon forgotten. The Historia silense, written around 1115, does not even mention him in its version of the division of Sancho III's realm. It even records that Ramiro was given the "remote" region of Aragon on account of his illegitimacy, despite the fact that Gonzalo's division was more remote than Aragon and his legitimacy unquestioned. The anonymous Chronica naierensis of about 1200, basing its account entirely on the Silense, likewise ignores Gonzalo and blames Ramiro's position on his illegitimacy.[11] The Liber regum, also from around 1200 but independent of the Silense, nevertheless shows no awareness of Gonzalo.[12]