The National Electric Code requires metal mast grounding. (NFPA70)
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I wouldn't want to present a damage claim to my homeowner's insurance involving a code non-compliance event.
The NEC would apply only if the local jurisdiction says so. And some local jurisdictions actually add (or subtract) requirements. For simple example, Chicago's requirement for conduit everywhere.
And whether your homeowner's insurance would balk at paying is a question of how the policy is written. Most policies don't explicitly require code compliance.
If lightning does hit your ungrounded mast, chances are good that your house itself will suffer some pretty significant (bad) damage. Give it a path to ground and you improve your results.
Some experts argue that, in some types of events and surrounding environments, grounding the mast significantly increases the probability that lightning will hit it. ["Lightning Rod"]. There are lots of experts with differing expert opinions, and research/evidence to back them up.
Many local jurisdictions have deliberately decided to
remain silent about this issue, in their local code. Their legitimate fear is that if someone is "code compliant" and gets damage from a lightning strike, the jurisdiction might be sued because they "required" something.
