I have been working in the area for 38 years, so I have dealt with a lot of sociolinguists, political scientists, and the like. The evidence is overwhelming.
The sociolinguist Louis-Jean Calvet, for example, says that cities devour languages. In his opinion, people in the same city will all speak the same language in 15 years if nothing is done to protect the minority language. Another has said that languages in contact are languages in conflict, and the stronger language will win.
The evidence is overwhelming. There is no way around it. If there is no legislation to protect the use of a language or to provide it with space, the stronger language will dominate. That is even clearer here, in North America, where we are surrounded by 330 million anglophones.