As long as they are not F1 crosses, (or F2 etc) they will breed true
from seed as long as they can't be crossed with plants in nearby
gardens. With nearby gardens growing the same crops you do run the risk
of crosses with that variety, which may or may not be a bad thing.
Any crop that is not F1 hybrid etc. should remain true. Many F1s are,
in fact, sterile so will never produce viable seed.