Yup, that's why there is a 75% threshold so your scenario won't happen. 75% is more than enough. It means on the worst case, 75% agreed to leave at most 25% behind. I doubt 25% will stick with the old chain anyway.
I guess you didn't closely follow about what happened with NotXT.
I can guarantee you that there will be fake BitcoinClassic nodes created so that it seems that 75% is achieved and then after one day - that 75% will disappear (and this is why all exchanges will simply stop exchanging as they know that this will happen).
Fake bitcoin classic nodes would not be able to raise the percent of support since they aren't actual miners. At the end the amount of hashrates are mattering.
And when a fork happens then when support for this new system raises a high value which means everyone will switch then since it is very unlikely that they will drop again then.