First, my hopes that the doctors will prove wrong, and that the funds will enable you to find a cure or enjoy life to the fullest until the end.
The accelereated death benefits provisions that you refer to have been around 12 years or so -- I was involved in one of the very first plans. Typically the group policy presumably permits such payments only if the doctors (yours initially, and the the insurance company's who often review the records) project a life expectancy of less than 1 or 2 years, depending on the insurer. In that case there would be no tax effect if there was a withdrawl, as Congress has permitted withdrawls free from tax in those circumstances.
I do not know about creditors' ability to attach the funds if they learn about it, but it seems to me that learning about it is not easy and if you got the money and spent it on care there is little the creditors or a court could do aqs a practical matter, given what the doctors have predicted.
