They also make refactoring much easier. Renaming a function or variable and having all "true" references renamed (not just things with the same name but in a different scope), for example.
Incidentally programming in a more functional style reduces the need for this kind of thing. it doesn't eliminate it though so it can still be a source of runtime bugs when typos creep in, that's a trade off you have to make.
For any life-critical system you want first and foremost to have a battery of end-to-end tests that run the software on the target hardware under various operating conditions. No amount of software-only testing/formal methods will give you this part.
Then, you want to have a formal specification of your program that can be run through a model checker - this would be the industry standard, though, if you have a team of PhDs at your disposal, you could also try to go with full formal verification a la Coq.
Finally, you want unit testing, integration testing, and possibly a type system to help day-to-day development. But do note, none of these should be critical for assuring the system works as indended - if typos in your code aren't caught by your end-to-end tests, what hope is there that they will catch complex dynamic behaviors?
Safety critical systems are quite different from the vast majority of software systems, and raising them as an example in a general programming argument isn't really fair. There already are safety critical certifications that are mandatory for many aviation and healthcare related applications. They generally utilize heavy testing, model checking, and supporting documentation. Very few commercial industries operate with this much attention to quality, basically because it's too expensive.
You are right though, the standard for that type of software is very different from regular programming.
Still, we shouldn't forget that even the strongest typing can't substitute testing. Most likely, even if you had a formally proved system, which is already much, much more difficult than any other kind of regular software development practice, you would still want some amount of testing to go with that system before putting it in production.