That may not always work; it depends what the return value of some_long_running_shell_command is when it receives a SIGINT. And it also depends what it returns when no SIGINT is given. "find" for instance returns (shell) FALSE on SIGINT, but also FALSE when it cannot process all files (for instance when the process doesn't have permission to decent into a directory). And (at least the 'find' found on my computer) it doesn't specify the actual exit values; just 0 and non-0.

So, checking return values may work, but be aware, it will depend on the actual command run whether it will.