Anyone who works at least eight hours a week for an employer on average is covered by obligatory insurance against non-occupational accidents. This insurance is valid for as long as the person is entitled to at least half pay.
If an employed person stops work temporarily or permanently, they continue to be covered by insurance against non-occupational accidents for 30 days after the employment relationship ends. If, for example, employees take three months' unpaid leave, and are not therefore working for three months, they are still insured against non-occupational accidents during the first 30 days of their unpaid leave, after which cover ceases.
Helsana's extended insurance enables employees to extend their cover by a total of 6 months, so they get all the benefits provided for under the Accident Insurance Act (UVG).
Good to know: You're required by Art. 72 of the Accident Insurance Ordinance (UVV) to pass on to your employees any information you receive about your accident insurance. This includes an obligation to tell your employees about the availability of extended insurance.
Here (PDF, 40KB) is the information sheet on extended insurance under the UVG.