If you'd saved frequently, a swift break and old would do the trick. Otherwise, ouch.
Uh? It's if you didn't save frequently that you had to rely on 'old' and the dreaded and unrecoverable 'Bad program' error that sometimes bit.
If you saved frequently then a reload from disk would do you fine.
You needed to be in mode 7 to use all the teletext like operations; but in the graphics modes (0, 1, 2, 4, 5) you could send vdu commands to plot lines and so forth. How we laughed until we got punched.