Nothing would have happened, because that was not an invasion but a raid. they did not plan to stay they only wanted to plunder. Thus if they had won at Tours and Poitiers they would have returned to Spain with rich plunder and would have returned for more some years later. And then the Franks could have stopped them.
But it could have stopped the career of Charles Martel.
Agreed, it really depends on what happens to charles martel and the franks.
If martel dies there and the frankish empire doesn't stumble into an equally vigirous ruler than that has huge consequences.
Tours wasn't anything more than a raid. But as a result of winning there Martel was able to campaign continuley against the moors and drive them back to the pyrenees and also bring independent toulouse back under the frankish wing.
And his son was able to claim the throne of france and his grandson christianised germany and founded the holy roman empire and with that the concept of 'christendom'. Also Martel's encounter with heavy cavalry at tours led him to creating the first heavy cavalry units in western europe in response which would have been delayed possibly by decades by his death with huge consequences.
The carolingian dynasty which really got roling at tours was a huge part in the history of france, italy, iberia and germany and a huge reason for why the islamic conquests reached their natural limit and why the counter attacks of the reconquistia and the crusades could take place. They were the second most written about christian force in islamic writing after only the byzantines and generally were recognised by the muslims as the most powerfual force they'd faced in western europe. A resounding defeat at tours could gut that enemy by wiping out it's army and it's primary leader.
However if martel jis just forced to retreat but remains alive and in good standing with his army then you probably see only minor differences. The improtance of the battle is less that it was won but that martel was able to uae it as a springboard.