Yes, travel insurance is close to essential for a trip to Guanaja, the easternmost of Honduras's Bay Islands, and the honest core of the answer is distance from serious medical care combined with genuine diving risk. Guanaja's reefs are a real draw for visitors, and diving-related injuries are exactly the kind of incident that turns a routine island trip into one that needs proper evacuation cover.
The island has only basic local clinics, and anything beyond minor treatment typically means transfer to La Ceiba on the Honduran mainland, with more serious or complex cases sometimes requiring further evacuation to the United States. Confirm your policy explicitly covers medical evacuation and international repatriation, since the multi-leg journey off Guanaja - not treatment on the island itself - is the part most likely to involve real cost.
Diving is the main activity risk here, and standard travel policies do not automatically cover it at every depth or certification level; check that your policy names scuba diving specifically and confirm any depth limit before booking dives, since a policy that only reimburses land-based injury misses the point of a trip built around Guanaja's reefs. Confirm the same for any dive-related decompression treatment, which is a real possibility this far from a full hospital.
Hurricane season, roughly June through November, adds a further layer of risk for this stretch of the Caribbean, with the possibility of disrupted flights, boat transfers, and short-notice evacuation orders. Trip-delay and cancellation cover matter more during this window, so check how your policy defines a named storm versus routine weather delay before booking mid-season travel.
Keep any clinic paperwork, dive-operator incident reports, and receipts for emergency transport, since claims from a remote island like Guanaja depend heavily on documentation collected on the spot. Many policies require notice before major expenses like evacuation are incurred, so review your policy's claims process before you travel rather than after something happens.