Nothing changes really : the non-french languages were still around in relative wealth around 1900. What made them disappear was less the french-only policy (that put them in a diglossia situation, a lower one) than the more and more global economy.
Furthermore, not supressing the other languages was quite the regular republican goal : they wanted to get rid of it in the public discussion, but they didn't saw any problem by having lower classes still using it (as it reinforced the class differenciation).
The only ones to have claimed a supression of non-french languages were the majority of Jacobins but 1)They never had the power to enforce this program 2)Their propaganda, political program etc was made in non-french language in the regions concerned.
Apart having a complete reverse (France HELPING the non-french languages), you won't have anything, maybe less regionalist bitching about the responsability of the state and more trying to see their own failures.
The linguistic policy wasn't a racial one (except in very special cases) and didn't lead to a real discrimination against the individuals, except culturally.
So, I would say no big changes. Maybe more speakers, and more insitutionalised non-french languages. But it could be even worse than the actual situation : having institutionnalized occitan would lead to an occitan more influenced by french, or a breton language using french referents.