Considering that so many died, was magellan's voyage a success? why?

Yes, was successful.

Explanation:

If the legacy that was left from the voyage, it was very successful.

They discovered the Philippines, "new" animals were observed such as llamas and penguins, the biggest ocean on earth's name was giving by Magellan "pacific", places in astronomy are named after him: Magellanic Clouds (galaxies), Magellan Crater (Moon) and Magellan Crater (Mars)

answer; /// i do believe that its napolean's conquest of spain;