The Magyars were by 955 in serious decline. Over the previous half-century, the Germans had adapted to their tactics and had constructed a formidable system of defense-in-depth throughout the Bavarian march. Just a few years before Lechfeld, the Duke of Bavaria had raided Magyar-held Pannonia and forced the Magyars to pay tribute to him, the opposite of what had been going on for decades previously.
Lechfeld is best thought of as a last-ditch attempt to disrupt a worrying trend of German supremacy and Magyar defeat. The Magyar leaders probably did not attack Augsburg because they actually wanted Augsburg; more likely, the siege was intended to force Otto into the field (which was successful) and defeat him in open battle (which was not). Even if the Magyar plan had been completely successful, however, they had neither the interest nor the capability to conquer Germany. Even in Italy, a far weaker state than Otto's Germany, the only city they successfully captured was Pavia, which they sacked and then immediately abandoned. They were, after 900, a raider-state, which existed to plunder territory rather than to conquer it. Otto's death in battle and the destruction of his army would have allowed them free reign to raid in Germany and Italy as they had done in the recent past, but I highly doubt the geographical area of Magyar settlement would have changed much, if at all, and the German reverse would have been only temporary. Destroying Otto's force would not also destroy all the Ungarnwälle (the system of anti-Magyar fortresses), nor would it destroy the local levies which manned them, nor the private armies possessed by dukes, counts, and bishops across the kingdom, nor would it have changed the basic fact that by 955 the Germans knew how to fight the Magyars and were by the 950s winning more battles than they were losing. Ultimately Germany would still likely end up being the hegemonic power of central Europe, not Hungary; a botched Lechfeld would delay this, but not avert it.
The biggest effect of this scenario would be Otto's death, because by 955 he was not yet emperor and Berengar II was still in place (albeit shorn of Verona-Friuli). In a worst-case scenario, Otto's death means the kingdom is plunged into civil war and subject to further Magyar raiding, which may mean that Berengar has a chance to regain his position in Italy. The failure of the empire to form under Otto would be far more consequential than a few more years/decades of Magyar raiding allowed by a Magyar victory at Lechfeld.