Yes, yes and yes.
You work hard to earn your vacation, and it isn't cheap. Neither is diving. But trip insurance is - and it may even be provided by your credit card company (worth checking out).
Even if it's not, trip insurance usually costs pennies per vacation day and can save you a lot of money and disappointment.
For example if you have to cancel your dives due to airline delays, injury, bad conditions, lost luggage, injury, hangover (happens a lot and we won't tell the insurance company if you don't), your trip insurance will cover it.
Cancelling diving due to bad conditions is worst case scenario and of course, we do our best to reschedule in such events. But it's not always possible, so getting your money back under your trip insurance policy removes some of the 'ouch'.
Long story short? Yes, take out trip insurance!