I haven’t looked at the new case yet, but from memory the cases about tribunal discharge all took it for granted that accepting the Hobson’s choice of being deprived of your liberty outside hospital wasn’t valid consent for Article 5 purposes.
The MOJ and MHT interpretation that the new deprivation of liberty conditions cannot be enforced except by recall, and so agreement is at all times required, is daft but is a separate issue (Enforceability of new deprivation of liberty conditional discharge - #13 by Jonathan).
Shackling ourselves to the European Convention instead of just writing our own laws is the source of all these problems.