You are just a click and a day or two away from getting your physical bars delivered to you. If the world goes to crap fast enough to rescind the guarantee within a few days without any hint of it the news, then you've got much bigger problems than not having access to your physical metal. War breaks out overnight? The government have more to worry about in the first few days than enacting legislation to grab peoples gold (which is a drop in the bucket in the national budget, they'd make vastly more freezing super or bank accounts or something)
And personal physical ownership is vastly more risky, give the many robberies stories and also the shutting down of private SDB companies like Perth Bullion.
If you are worried about a true SHFT scenario and you want physical on your possession at all times then a few rolls of kooks and cash in your prepper bug-out bag will do the trick. The rest of your wealth in metal is safer in government backed facility.