Is travel insurance mandatory if planning a tour abroad?

This is not mandatory for traveling abroad. You don't need to buy a travel insurance policy when you're traveling abroad. However, you should always be ready for the unexpected circumstances during your foreign trip. A travel insurance policy may come handy in that situation.

NO, as per my knowledge, travel insurance is not mandatory.

To get the VISA, you might need to purchase a basic travel insurance policy, if your existing policy doesn't provide any or adequate coverage. However, it might depend on the policy of the country you're visiting. So, it's better you check out the rules and regulations beforehand.