I personally believe he would not have been forced to resign if the tapes were not available.
President Nixon was one of the most popular leaders at the time when he won elections in a landslide victory. Though he prayed on racial discrimination to gain votes in the south of the county, he actually won by one of the largest landslide victories in the US history.
He was also able to accomplish numerous economic and geopolitical wins for the country and was overall a very powerful president with a huge support base.
Without the tapes, Nixon would quite possibly have survived well into at least ending his 4 year term.
