Existing government revenues won't change. The extra hours now worked will not provide the government with additional future revenues.
If we suppose that the restaurant owner is better off under the new system, then we might see him shed an entire shift. The remaining two waitresses will then provide the same level of service that presently exists for the full 70 hours. Two waitresses will be highly paid. Two will become unemployed. The employer will see little net change and the government will give up revenue which might previously have been used to pay unemployment to waitresses.
Sarkozy's proposal is a pure, unadulterated supply-side inducement to increase production. It will allow people to work (produce) more and allow them to keep everything they earn above 35 hours. A very powerful inducement, indeed.
As the author mentioned, had the owner been less harried she might have convinced him to have dessert and another glass of wine. As it is, she lost several euros of income and profit.
Why Sarkozy's proposal would spur a business owner to cut his hours in half and lay off 2 employees is beyond me and hasn't proved the case when marginal tax rates have been cut in the U.S.
In my example, the government loses all payroll taxes associated with the two waitresses that are no longer employed.