I'm terrified this is going to become our new way of life and can't think of a single, workable solution.
The Front Nationale can think of a single, unworkable solution and unless the non-fascist French politicians come up with something which is reassuring and effective in the meantime, you can either say hello to President Le Pen or at the very least you can get ready for a lot of French local elections to result in Front Nationale mayors, who in France have a lot of power.
The first, and most important, job that a government does it stop its citizens from being killed. Governments that appear indifferent to the safety of the populace don't tend to last long in office. Hollande has so far done very little, because there is very little he can do, following a long succession of random killings which all have one thing in common. It's very hard to deal with unless you're a fascist, but even the fascist solutions don't work (all that repression, none of the results).
Unfortunately, France has a prepped and ready to go fascist party, and Marine Le Pen has been polling around 30% before the recent atrocities. If you want to say "oh no, of course France will never elect an FN president", you might like to think how much chance Donald Trump was of being the Republican candidate. Do you feel lucky?