Swift shipped source-breaking updates earlier in its lifetime. I honestly don't really know of a story where a source-incompatible update killed a language. People grumble, then they move on.
Perl, with the Perl 5 -> Perl 6 (later Raku) transition? Fortran, with the F77 -> F95 transition?
> I honestly don't really know of a story where a source-incompatible update killed a language.
Perl. I mean, Perl isn't strictly dead, but its share of the market plummeted. Python almost certainly would have suffered a similar fate if it weren't for the explosion of interest in scientific/numeric computing (which more than made up for massive attrition to other languages, including Go).
Death may not come as swiftly (heh) as you think. I know a few people (including myself) who, when deciding which language to add to their toolbox, had decided against Swift because of its reputation as “that language that always breaks code”, among other reasons. There are just a few anecdotal data points, of course, but I don't think it's controversial to say that a history of messy updates definitely makes new people less likely to learn a language without an absolute necessity.