Maybe, or maybe not. But it will certainly kill the community they've built up, and squander a huge amount of goodwill. Why would anybody who's interested in supporting or using an independent browser (read: techies) choose one that nobody can contribute to? Not to mention how the sponsors might feel about this.

> Why would anybody who's interested in supporting or using an independent browser (read: techies) choose one that's only source-available?

It's not source-available, it's open-source.