It depends on the what the browsers end up doing. If they just surface a select your search engine dialog during set up, most people will just select google and nothing will have changed besides the cost. If they set a non-google search engine by default, they will lose ad revenue because of people not bothering to change the default.

Depends on the default search engine. Many people went of their way to download a web browser that wasn't Internet Explorer for many years even though IE was the default.

If the default search were randomly assigned and Google investors were nefarious the investors (not Alphabet) could simply help launch 30 different subpar search engines. Then if a user landed on one of those as a default search engine: the user would switch to Google.