It is far too easy to create a softlock cartridge.

RUN() -- Softlocks program if run from Splore. The only
      -- way to stop is by closing PICO-8 entirely.

Of course, if run from the command line you can always just press ESC and everything will be fine. But I've tested this by running from Splore and there is no escape.
Try it yourself! Just make sure that you saved your work.