I have just purchased a dwarf weeping willow, Salix caprea Kilmarnock. I noticed it is top grafted, I assume so it does not grow to too tall and also keeps its shape. The question is, if I take cuttings from it and let it grow naturally without using the grafting technique, how will it turn out?

This willow is incredibly easy to root. No rooting hormones are needed. Taking cuttings from the weeping part of the plant will retain its reluctance for upward growth. A cutting grown plant will be a groundcover willow, unless you physically train it and stake it upwards.