These are production platforms, not drilling platforms. A production platform like the one mentioned in the article gathers oil and gas from dozens of wells connected by a system of piping laid on the sea floor. As such, they'd have no way to plug a well. Operators use mobile rigs to do a "P&A" (Plug and Abandon). There's no way that the permitting authority would allow the well operator to abandon any wellhead without plugging it, no matter who they'd sold the production platform to.