Ruthlesstyrant said:
Let me think about the immediate consequences:
Spain would become a base for the Visigoths for some time, and probably be attacked by the Byzantines if they could tighten their grip on North Africa, and most probably by the Franks who were catholic (as opposed to Visigoth Arian Christianity).
The Visigoths converted to Catholicism under King Reccared in 589, more than a century before the Muslims arrived. So, no Religion wars between Franks and Visigoths.
On the Byzantines, they had constant problems against Sassanid armies, Middle-East rebellions and Arab
razzias in modern-day Jordan. Only a new "Ethernal Peace" and a new Belisarius could bring back the Byzantines to Spain, but it was very improbable. By the early 700s, the Visigoths wiped out the Byzantines even from modern day Ceuta, in North African coast.
The Visigoths had actually a good half feudal, half Roman army by the time. Their only weakeness was that the Monarchy was elective rather than hereditary. This caused many royal assassinations and civil wars, like the war between the new King Roderic and King Witiza' son Agila that started in 710. Agila was outnumbered and without external intervention he never could win the war against Roderic. He never would called for Byzantine help because there was still the rememberance of another Byzantine intervention in 552 that ended in treason and led to the Byzantine occupation of Andalusia. However, he called for another traditional mercenaries, the Franks, but Childebert III refused gold for his help and asked for the province of Septimania (modern Languedoc). Agila didn't accept.
Then Agila and the other Witizans asked for help with the third option, the Muslims, and ironically this ended with the biggest treason in Visigothic history and the anexation of the Iberian Peninsula to Ummayad Caliphate.
Without Muslims, there could not be third option, because the Berbers only would be a bunch of tiny and weak tribes. The possible consequencies are two:
1- Agila newly asks for the Franks and accepts the anexation of Septimania. However, at this time Franks were not very strong as under Clovis or Chalemagne reigns. The war would be extended for many years, devastating north-east Spain, but I think that Roderick would be emerged victorious due to geography (just see the Pyreenees + Ebro River natural double wall). However, Septimania would be annexed by the Franks anyway.
2- Agila resigns. This have two variants:
2.a. Agila is executed along his major supporters or
2.b. Agila becomes another man of Roderic's Army in his campaign against Basque rebels.
Later, it's possible that a strong King like Roderic introduced the hereditary monarchy, like King Liuvigild (569-586) was ready to do. The following is an interesting alternate Iberian Peninsula, unified and ruled by a Germanic dinasty but withouth any "Dark Age" like other Western European states. The Visigoths kept many knowledge from their Roman precessors and had great intellectuals like Isidore of Seville, for instance.
I think that this surviving Visigothic kingdom would supported Charlemagne's campaign against Lombards due to their Catholic faith, but never would be an ally of the Franks.
Sorry for possible grammatical mistakes, English is not my native language.