International law dictates that no country can make someone stateless. It is with deep regret that I have to say that Shamima Begum is a UK citizen. Ergo, the UK government cannot withdraw her citizenship.
I think that the then home secretary, Sajid Javid, knew full well that he could not legally remove her legal right to be a UK citizen but did so anyway and was hoping to put her in legal purgatory for the foreseeable future in the hope that she might have some kind of unfortunate accident in her Syrian refugee camp. Problem solved, so to speak.
However, if she didn't succumb to said happy accident, his revocation of her passport was always going to be legally challenged and likely succeed. At this point I think it's inevitable that she'll return to the UK.
To be brutally honest, I really don't care any more. Shamima Begum is – in the grand scheme of things – not a big deal. There are already thousands of fundamentalist Islamic lunatics running around the UK who are a clear and present danger to the men, women and children of this country. These are individuals who may carry out another Manchester bombing at any time. There are reputedly 3,000 of these insane Islamists who are deemed to be the most dangerous Jihadis but there are another 40,000 who the police and MI5 suspect are involved in the promotion of Islamic terrorism.
Shamima Begum is a nobody. The physical risk she poses to the UK is minimal but her PR value to the existing Jihadis and their supporters is significant.