So sorry to hear that. A photo or two might help. Hard to comment here without any. A frame failure can usually be repaired. If the A-frame separated from the main frame, it's a straightforward repair. This happened to someone on this forum and he welded it back together. Can't find his photos at the moment.
We had a brand new TT a number of years ago and discovered a frame problem the day after we owned it. At first, Lippert said "it was within spec.". I knew it was total BS so took it into a gov't certified frame & axle shop. After getting a report and submitting it, we ended up getting the whole TT replaced under warranty without a whimper from the TT manufacturer.
Telling someone that they overloaded their TT is a common tactic by Lippert. Before they even know what the problem is, you'll hear that. If you had taken the TT through a scale when fully loaded, that would have helped.
I HIGHLY recommend you get a reputable frame & axle shop inspect it. They will be able to tell you what it will take to do the repairs. It might even be that it's not as bad as you think.
What type of frame? There is one type that has I-beams made from 3 pieces of 1/8" mild steel welded together lengthwise. These look like a regular cold-rolled I-beam but you can feel the continuous welds and see them. These 3-piece I-beams flex a LOT more and are a poor design and are more susceptible to problems. If you have this type, that's a major factor to start with.
When we had our TT inspected, they also found a number of other issues with it that we hadn't expected. They ended up saying it was the worst frame they'd ever seen and that it could never be corrected to what it ought to have been like from the factory to start with. It had the 3-piece I-beam design.
If the TT manufacturer didn't say anywhere you can't tow with one or more full holding tanks, you shouldn't have a problem with doing that and folks do that all the time. If anything happens, it's normally just the tank supports that fail. However, note that some TTs have a low cargo carrying capacity and just one full holding tank could put you over the GVWR, which would happen with us. Depends on how much you load into the TT though.
Interestingly, frames do not have any ratings or specifications and there are no industry standards/codes they have to comply with. There are no specs on how heavy or long a TT "box" can be that sits on a frame. As a result, Lippert can build frames however they want and answer to no one. Axles on the other hand have ratings, specs and detailed info. available online. People have been having frame issues for years and Lippert continues to crank out the same frames with the same build quality.
Don't believe any of Lippert's BS. Despite what they or anyone else may say, their frame quality can leave a lot to be desired. Their welds can often be substandard. Some never have issues. Frame failures happen more often than people think. (One reason is that if a TT gets replaced, the owner has to sign an NDA agreement.)