After a person has been missing for seven years, they can be declared legally dead most states. Sometimes this can happen a lot sooner, if it's reasonable to assume they were involved in a violent crime. Maura Murray has been missing for eleven years, now. Her father, Fred, has said several times he believes she was taken by a "dirtbag."
One reason to declare someone dead is so that you can sue public entities in private court -- Fred has wanted to hold the State of New Hampshire accountable (negligent) in their search for his daughter. This would have been a good opportunity for him to force some answers. But it didn't happen.
The most common reason someone is declared dead when they are missing and no body has been found is so that their property can be divided amongst survivors in probate court. Maura likely didn't have more than a couple hundred dollars to her name -- though it is possible that Fred or another relative set up a trust for education or life insurance or something. So, dividing assets was really never an issue.
Except it kind of is.
When Maura's mother, Laurie, died (on Maura's birthday) in 2009, Laurie's estate wound up in probate court with Fred as the executor and Julie as an agent. At this point, it would have been in everyone's best interest to have Maura legally declared dead. And yet it doesn't appear that this has happened.
One reason might be so that Maura can continue to work.
If someone is declared dead, the Division of Medical Assistance and the Department of Revenue (for Mass, here) would be notified. The IRS could be notified, too. That means if Maura is alive and working, she could not file taxes or sign up for welfare or social security. All this becomes very problematic.
When a person is declared dead, family members and friends must be interviewed and provide affidavits under record about why they believe this person is deceased.
In any event, the court was required to do their due diligence to figure out if Maura was still missing when Laurie passed away. It's unclear if that took place.
(Special thanks to Boston probate attorney John Dugan)