Al-Andalus was probably doomed from the moment the Cordoba Caliphate dissolved in the decade of 1030's. It is impossible that the chaotic collection of statelets that followed it could have resisted the now bigger and more powerful christian states.
However, the Reconquista was a very irregular affair, where short outbursts of activity were followed by decades of stagnation. It is not impossible that, with changing circumstances, the christian states would have allowed a muslim remnant in at least Andalucia. From 1250 on, both Portugal and Aragon had dropped out of the Reconquista, leaving Castile and Granada alone.
In fact, that is what happened: the Reconquista ended officially in 1492, but from 1250 onwards, Castille alone could have crushed Granada like a bug if they had wanted to. They just didn't because, until the Catholic Kings took over, Granada was more profitable to Castille that way. The only major war between the conquest of western Andalucia in 1230-1250 and the final Granada war in the 1480's was the Benimerin wars between 1340 and 1350. Between 1350 and 1480, Castile just didn't care about Granada. Juan II in 1410 even signed a treaty with Granada to clearly delimitate the borders.
So, one chance to have Al-andalus survive if at least ina weakened state, is to butterfly the Catholic Kings away and have Castile accept Granada's existance as a fact, at least as a tributary.
The best chance, however, is to have the almohads or almoravids decisively defeating the christians and cementing their rule over the southern half of the peninsula. Despite the fall of Toledo ensuring an easy access to the central plains for the castilians, muslim dominance over what is today La Mancha would not really be over until after Las Navas de Tolosa in 1212; and muslim control over Valencia and Murcia could have lasted much more if James II the Conqueror of Aragon (a sadly overlooked badass) had not gone in his conquering rampage between 1229 and 1250. The almohad victory at Alarcos in 1195 crushed the castilians, who evacuated most of the central plain south of Toledo. If the almohads had been able to exploit this to retake Toledo -and it is theoretically possible-, they could have reversed the situation to the state where it was a century before.
Another last chance for the muslims is to decisively defeat the allied christian armies at Las Navas de Tolosa, which was a very close affair if we are to believe christian chronicles. After Las Navas, there was no hope for the muslims: the central plains would forever be in christian hands, the door of Andalucia was open, and, most important, what had been a war for land and prestige for the past 500 years, became an ideological, religious war. A decisive muslim victory at Las Navas could have ensured muslim domination of Andalucia by at least making the castilians accept that they could not conquer it.