Broadly speaking, there are three possibilities here.

1.) Maura is going to a general, unspecified location in the White Mountains to commit suicide. This theory would be supported by the fact that the accident wouldn't have deterred this, and by the fact that no one has come forward saying what the actual destination was because there wasn't one. She was close enough to where she was going at the time of the crash if this is true. The calls to various vacation properties in the region don't necessarily rule out that she planned to go off into the mountains alone and not return after arriving there. If this was her plan, probably no one would know.

Going against this possibility is the refusal of Kate and Sara to talk, and to a lesser extent, Fred's behavior. It could be argued the contents of her car suggest being prepared for an overnight stay. The withdrawal of nearly all her funds from the ATM is really puzzling in this instance. Also, why does Maura buy as much alcohol as she does if this is the plan? Why would she obfuscate the situation intentionally? This would just cause her family and friends pain and uncertainty.

2.) Maura had a White Mountains destination in mind, whether to take a few days to gather her thoughts, or to rendezvous before running away, or to plan to die in the woods. On the way there, maybe she accidentally dies in the woods, purposefully dies in the woods, a wild dirtbag appears, or a tandem driver comes to save the day. In any case, there was a plan. The calls to various properties strongly support the idea that she is headed to a destination in the region. She is packed for a short trip. She has lots of booze, cash, and a full tank of gas. Fred thinks this is what she intended, and I do think his intuition carries weight.

Given the time Maura spent with Kate and Sara very shortly before her disappearance, it seems likely they would know where Maura was going if she was just planning a vacation. The idea that someone is planning a trip somewhere and NO ONE knows is not all that believable. She may have been embarrassed about deciding to leave UMass, but you'd think someone knows where she was headed in the short term. Why wouldn't Fred know what her plan was if she wanted to take a 2-3 day break?

The lack of any kind of booking is something of a concern, but Maura might have known that there would be venues that definitely would have had vacancies. Investigators should have looked at all the rental properties for renters who may have had ties to UMass if she had any kind of associate who was nearby. I could see the police withholding this though. Billy clearly has no idea specifically where she was headed, as his phone records show.

Kate and Sara's behavior gives the most fuel to the runaway theory here. Is there any reason the police wouldn't say that Maura was headed to XYZ Lodge in Stowe if they knew that to be true? Why wouldn't her friends say where she was going if there was nothing to hide, or if that information could help find her. They are lying to investigators, and that lie could easily include what the destination was.

3.) Maura has some other destination in mind and the evidence for this is not available or the people who know won't talk about it.

This is a possibility but it takes a pretty big leap to get there. There's no evidence other than people who won't talk, and it requires someone to believe in deliberate red herrings from multiple people involved.

My conclusion is that the suicide theory is not very fun because there won't be closure aside from a found body. That's one reason why many don't like it. It takes the fun out of being an amateur detective. If a suicide is what happened it's not likely that any new info will be satisfying.

People like the other theories because new info could really fill in a lot of gaps. As has been said a lot this week, what do Kate and/or Sara know that we don't?