The tunnel linking the mountain to the main forces was never completed
The day the Americans invaded, 11 miles of a planned 17 miles of tunnel network had been dug.
The Japanese supply was inadequate. Troops were supplied a 60% of the standard issue of ammunitions sufficient for one engagement by one division, and food and forage enough for four months.
IJA had 21,060 total men under arms vs. 110,000 USMC men
So, let's give the Japanese the following:
Tunnels are completed as designed
Troops have sufficient ammunition and food
50,000 IJA troops
How is the battle impacted? It's still going to be a loss for the IJA of course.