Tim Miller is a good man. Regardless of what he's said in the past, everyone is human. He has helped so many families find closure. If i had a loved one go missing, i wouldn't hesitate to call him and TES in for help.
It would be sad to see him stop TES, he's done so much good for people.
As for him saying Haleigh is dead, i agree with him. Statistically speaking if missing children aren't found within the first 24 hours the odds of them being alive decline drastically. Look what happened with little Somer. Tim knows this, and given the certain circumstances of this case (Misty not cooperation) there is only so much one can do unless Misty tells what really happened that night.
There are a lot of other missing people that need TES and TM knows this. If Misty would cooperate, i'm sure he'd come back to search.
His comment about Misty calling Donna 3 times suicidal, is very important. IMO, (this is just my opinion, if you don't like it, please just ignore it) Her being suicidal could have to do with the scrutiny and stress she is under as she won't tell the truth on what happened, also Misty being suicidal could be taken as a sign of guilt.
She seems to have a lot of underlying problems that would make her depressed, i seem the importance of trying to get her help anyway possible in case she decides to really kill herself. If she does, the truth will never be known about that night.
Also, the families do have to come to acceptance that Haleigh may be deceased.
There are numerous ways to get rid of a body and it doesn't take that much imagination to know which ways. Especially in Florida with alligators and the Altantic. Not to mention numerous undeveloped woods.