The nature of Vane's personal relationship with Eleanor may, indeed lead him to make a rescue attempt. In fact, Flint might encourage him to take that route just to get him out of the way while he concentrates on the defense of Nassau. On that topic, I've got some ideas.
I don't know why the Nassau fort cannons had a range shorter than the range of a man-of-war anchored in the harbor, which seems to make those guns kind of useless. Flint took advantage of that mismatch to decimate the fort, an action which surely could be repeated by the Royal Navy when it arrives.
Now, if I were Flint (argh! the pirate's life!), here's what I would do:
- forget about repairing the fort. Any efforts there would be a waste of time and resources. As is, the fort's appearance might actually bolster the confidence of the navy officers
- salvage any still functional fort cannons
- move all but one or two cannons out of the fort and hide them along the shoreline within range of ships in the harbor. Add to that firepower as necessary by relocating cannons from the Spanish man-of-war
- wait until the English ships show up, and give them time to get comfortable in the harbor
- open fire with the remaining cannons in the fort, getting the navy ships to concentrate their fire on the fort
- open up with the shoreline cannons and sink the whole English task force before they know what hit them. Surprise!
Handed a defeat like that, the English Navy could conceivably abandon the whole idea of bringing the pirates to justice.
