Yes, travel insurance is worth carrying for any trip through Colombo Bandaranaike, the main international gateway to Sri Lanka, and the honest reasons here are cost and season rather than any single dramatic danger. Sri Lanka runs on two separate monsoon systems that hit opposite coasts at different times of year, and that split matters for anyone planning a beach or hill-country itinerary beyond the airport itself.
Colombo has private hospitals capable of reasonably good care by regional standards, though quality and cost vary between facilities, and treatment for a foreign visitor without local coverage can add up quickly. A policy that settles directly with the hospital, rather than one that only reimburses you afterward, spares you from an upfront bill in an unfamiliar system; confirm which arrangement your policy actually uses before you rely on it.
The two monsoon seasons are worth planning around specifically: the southwest monsoon, roughly May through September, affects the west and south coasts around Colombo and popular beach areas, while the northeast monsoon, roughly October through January, shifts heavy rain to the east coast instead. Either window can bring flight delays, rough coastal seas, and flash flooding on inland roads, so check that your policy covers weather-related trip delay for whichever coast your itinerary favors.
Onward travel from Colombo into the hill country or wildlife parks adds ordinary road-travel risk rather than anything unusual, and standard medical and accident cover is generally adequate for that portion of a trip. Keep hospital invoices and any receipts for treatment or medication, since Sri Lankan private providers generally issue standard paperwork on request. Check whether your policy pays hospitals directly or requires you to pay first and claim later, and confirm the weather-delay benefit names monsoon disruption specifically rather than only generic flight cancellation, since that distinction matters most for a Sri Lanka itinerary built around the coast.