I was told some time ago that Tesla would very likely take Roadsters for trade-in. That may have changed by now, though.Assuming someone hasn't come to take my keys away by then, my current thoughts are to drive the Roadster for 3 or 4 years until it's too hard to get in and out of the car and then trade it in for a Model S. That would work well, assuming by then there is a market for used Roadsters.
Consider yourself lucky. Likely most Americans are dealing with rapidly expanding backsides.It would let me still practice my smaller footprint plan, but let my shrinking backside have a little more comfort.