Why would BD government provide "Sovereign Guarantee" to a foreign investor? If they provide that to any BD local company, then those companies will have no problem in arranging money whatsover. I dont see any reason for govt to do that even to a BD company.
Lets say Sahara took 16 billion dollar loan against the "Sovereign Guarantee" and instead of investing the whole money in new Dhaka city, they diverted a chunk of it in Dubai which they will for sure. At the end of the day if the project cant generate enough return then BD government will have to pay back the loan. No government in their sane mind will do that, and 16 billion? Even uncle sam will be shaky doing so.