Yes, travel insurance for Mahe is worth arranging, and the reasons are specific to what people actually do on this island: dive its reefs, sail between the granite islands of the Seychelles, and spend time on the water well away from a hospital. Mahe itself is the most developed island in the group, home to Victoria, the Seychelles' capital, and to the country's main hospital, so day-to-day medical care here is genuinely better than on the outer islands - but it still has real limits worth planning around.
Victoria's hospital handles routine illness and injury reasonably well, but for anything serious - major trauma, complex surgery, advanced cardiac care - patients are often evacuated onward, commonly toward South Africa, where private hospitals can manage cases beyond what Seychelles' own facilities are equipped for. That evacuation leg is the honest core of why cover matters here even on the most developed island in the archipelago: it is not that Mahe lacks care, it is that serious cases outgrow what is locally available.
Diving and sailing are the other half of the picture, and both are genuinely popular around Mahe and the wider Seychelles. A standard travel policy can exclude scuba diving beyond a shallow depth, or exclude sailing between islands on chartered or crewed yachts, so confirming your policy actually covers the diving depths you plan and any inter-island sailing you book matters more than it would for a beach-only stay.
On the practical side, keep receipts for any clinic visit in Victoria, and any documentation from a dive operator or charter company if an incident occurs on the water. Check whether your existing health cover extends abroad and to the Seychelles specifically, since a domestic plan rarely carries over cleanly to an island nation this remote from your home country's own hospital network.