You’re not seriously referring to Shamima Begum when you write these words?
She closed the door to her own home when she decided to defect to a state which declared itself the sworn enemy of the United Kingdom.
Don’t forget, this was an attempt (still ongoing) to establish an Islamic State. It is not unreasonable to conclude that Ms Begum considered herself a citizen of that state, and renounced all links to the UK to the administrators of that state.
What should the UK have done with the Soviet defectors of the 1960’s, who spied for mother Russia and swore alliegience to the Soviet Union? Should we just welcome them back with open arms if they changed their minds and decided to return to the ‘homeland’ they were committed to destroy?
Shamima Begum has not been made ‘stateless’ by the UK: she knowingly and willingly swapped her British citizenship for that of Islamic State. Her future is none of our concern.