Quite a hypothetical thread, no?
Looking at previous examples of Bristol's seemingly excellent management and the resources on their current site, then surely the zoo would've sent the elephant away if she was in her prime but still living in her old accomodation. As I understand it, Wendy was an old elephant, so it would've been easier for animal and organisation to keep her at Bristol until her death. A young or mature elephant would (theoretically) be easier to transfer and integrate into an existing herd elsewhere.
The site hasn't got the room for facilities which could cater for even a handful of elephants and Bristol wouldn't have kept a solitary mature elephant so a new enclosure on the current zoo would most probably be implausible