What do you mean zero demand? Unless oil supply drops below oil demand, there will be a STRONG demand for OIL STORAGE, which is what MMP does. They're not buying and selling oil, they're renting space to put excess oil. Seems solid to me for a while. This glut needs a home, and their business is to provide it. I think the market agrees. MMP has been going up.
Their storage is full up at present. Their pipelines are full. And Magellan sold three of their six marine terminals in January. And the marine terminals are where the substantial storage tanks are located. While the stock might very well have upside - it’s not necessarily for the reasons you think (ie; available storage to lease)