This „keeps working while it breaks“, does it have a name? It comes up in highly dynamic environments often like Smalltalk as you mentioned, but also Lisp, Erlang and others.
This has been implemented to varying degrees of reliability, granularity (in terms of preserving state) and utility. It's a common concept but I don't know the name for it!
Examples:
https://en.wikipedia.org/wiki/Continuation
https://en.wikipedia.org/wiki/Fault_tolerance
Maybe fault tolerance is the right word? But it doesn't imply that you actually modify and build the thing while it already runs.
An example of fail open design in the real world, is electronic magnetic locks at apartment complexes or business buildings. If the building loses power the doors demagnetize and unlock, then indefinitely remains open but failing because it is always open now. The opposite would be the building loses power and the doors fail close and lock the doors indefinitely when power is lost, and now people can’t escape.
a good read is ROC https://en.m.wikipedia.org/wiki/Recovery-oriented_computing