If we are to take it as it went OTL, a Biafran victory likely means an end to a united Nigeria. Northern Nigeria threatened to leave in 1956 - when the UK first wanted to grant independence - to wrest more influence in the coming state. Western (really southwestern with Lagos) Nigeria had been playing with the idea for more than a decade, and may've set secession in motion by promising to leave with Eastern Nigeria/Biafra (the leadership reversed at the 11th hour). A loss to Biafra may be the catalyst for more secessions, and the Nigerian project is no more
But if Nigeria stays together, it's still in no shape to fight for a complete reconquest. Its biggest revenue source is gone, good luck trying to pay for another war. Nigeria's best chance to take back Biafra completely is via a Soviet promise to fully back and see through a reconquest. Deeper Soviet involvement would however rankle the culturally conservative North (a majority of the army's from there), and the new military head of government (the last one being deposed following the loss to Biafra) would be even more beholden to it. Also the Soviets aren't going to get that involved unless Nigeria "progresses towards socialism" - the same military banned the CPN (Communist Party of Nigeria) in the first coup. Cuban involvement in Angola was a direct result of its long-time links to a guerilla movement. It doesn't have the resources to fight all over the continent, so we can forget about it in Nigeria.
A united Nigeria can recover part of Biafra though. IOTL, Biafra's minorities (30-40% of the population) weren't too thrilled with secession, seeming like trading one set of masters for another. Almost all of the oil production was in minority lands. Biafra going full majoritarian = instant secession. The Nigerians come in then restorers of lawful government/facilitators of adequate representation to those minorities, provided that they don't want independence themselves. The rump Biafra becomes Swaziland 2.0, and Nigeria didn't even need to fight a war. If the minorities do want their own state, it could easily be under Nigerian or British "protection". Oil interests could even facilitate intervention a la Katanga.
As mentioned before, mainly France can come to Biafra's aid. With Biafra's non-oil infrastructure bombed out, the French would be more than happy to make money off of reconstruction. France at this point would not only be aiding an ally, but also protecting French investments. Biafra's other new allies, though, are largely of no help. Rhodesia, with its own war of survival, is ruled out. The same for the Portuguese and the Spanish (who left the region in 1968). South Africa's "win African friends" initiative wasn't serious IOTL, a Biafran victory won't change that by much. Place the Nigeria-Biafra war 5-10 years later, when the apartheid regime was willing to do anything for its survival, and you may see heavier South African involvement.
In short:
Disintegrated Nigeria - no chance
United Nigeria - no chance for a complete reconquest, partial reintegration possible.