Three things.
1) The opportunity rovers were part of NASA’s faster, better, cheaper initiative, so they had to come in under a very tight budget. So keep it simple, minimize cost, minimize complexity.
2) I believe they did have strategies for extending solar cell life, but solar cells degrade over time in any case. At some point, just that degradation reduces the output to the point where mission is no longer possible. Dust storms just add to that problem.
3) Keep in mind that its 14 years into a 6 month expected life, and the solar cells are not the only thing that may be at or near end of life. Batteries, motors, electronics, bearings, and gears, all wear out eventually. I am sure that the focus of this report on the solar cells is omitting the tremendous effort by the operations crew that has gone into keeping the rover running for this long. At some point, one or more of these types of failures just puts you beyond recovery.
I don’t imagine it’s lost as they KNOW where it is.
Just lost communication.