Another day, another article about 'immigrants'. (https://www.dailymail.co.uk/news/article-10949305/More-2-000-migrants-storm-fence-Spanish-enclave-bordering-Morocco-chaotic-scenes.html)
Will the Europeans force their leaders to act effectively, not to mention the deportation of these 'immigrants', or Europe will die in silently in the coming decades?
Well the answer to your question is never, because European people have decided to commit societal suicide.
Having said that, I think that it'd be completely fair for Europe to expel all the non-ethnic Europeans from the continent. No due process necessary, just a plane ticket back to their country of origin.