Questions about e46 subframe problems

So recently I had my 2000 328i in for a clutch replacement, and while my mechanic was fixing it he noticed that my subframe is cracking and separating. I had suspected it was happening for a while before but I haven't had the time or money to do anything about it. So my question is what is the worst that can happen if I continue to drive on it as it is? And is there anything I can do to slow down the wear and tear? I can't sell it because I owe to much on it. My mechanic told me if I tell my insurance about it they would total the car, is that a good route to go or should I try to get it fixed. Thanks in advance for any answers.