From what I understand, here in PA, AAA does not always pay for accident tows, only mechanical breakdowns. Not sure about MA. My advice would be to settle and let the car go. Where are you going to park a totalled Prizm, and what are you going to do with it?
When a car is totalled here in PA, the insurance company purchases the car from the owner for retail value and receives the title. That is why they take the car, it's theirs. It is then sold for parts to a junkyard. The insurance company doesn't sell the parts at a profit, they sell the whole car to the yard for a salvage value, which is much lower than retail.
Insurance companies would go broke if they took some people's emotions into account. If the car is totalled, let it go and move on. I apologize for being so blunt, but dragging your feet after you hear from them won't necessarily be good for you in the end. Right now, storage charges at the tow yard may be accruing. No one wants to let this go on longer than necessary, because every day this goes unsettled it is costing more.
One reason why liability has not been settled is the insurance company may not have taken an official statement from you or the truck driver... or they may be waiting for the police report or other official paperwork. It should be simple to assign liability once the paperwork is in to them. I would take the rental because it is clear they were at fault, they just need to get all the information they need. It is not always the insurance company's fault when things take longer than we want. Believe me, we've had cars, totalled and not totalled, sit on our lot for weeks waiting for the insurance company to evaluate them, and the delay is usually because one of the drivers hasn't gotten back to them, or the police agency is working at a snail's pace.
I don't mean to sound like I am 100% for the insurance companies, I'm not. They each have so many rules and idiosyncracies for the way they want their estimates written it is unreal. Our shop has Direct Repair contracts with 13 different companies, and it is hard to keep everything straight as far as their procedures go. Some of them I do not agree with.
Good luck in a speedy resolution, Dodgefan.