This is disproportionately so much worse for Facebook, than it is for German/French users.
1) Let's assume that German/French users are absolutely shattered to lose Facebook. If they are that hurt, they will probably do at least a basic Google search to find out why they can't access FB anymore. And what they will find is that FB preferred cutting them out rather than not transferring their data to the US.
I suspect that people would be split between (a) surprise that FB is storing their data, (b) surprise that FB has been sending their data to the US, (c) shocked that FB would choose to end operations than not send data to the US (which would immediately make them suspicious why they want to send data to the US), (d) have jingoistic anti-FB sentiments, etc.
I can't see a significant cohort that would be unhappy that their governments stood the ground on their data not being sent to the US. Even if you don't understand why the governments did this, you'd be wondering what FB has to hide that they can't keep the data in France/Germany.
2) Many people may not see FB as such a huge loss. There are many alternatives that could fill their social media addictions.
3) If there isn't a huge outcry for FB, that would shatter the aura of invincibility FB currently holds in the social media space. That aura has already been marginally dented with their latest quarterly results, but to see FB completely disappear from the 2 biggest European economies and life continuing as basically normal will be a huge blow to FB.
It will raise a whole lot of questions everywhere else. More authoritarian regimes will threaten to cut out FB if they don't help censor, etc. the way those regimes want them to. Privacy focused regimes would hold the threat of cutting out FB if it doesn't impose greater privacy protection. etc.
I don't see how FB can win here besides France/Germany folding, which I seriously doubt will happen.