The NASA announcement, available here, said specifically, "After more than a thousand commands to restore contact, engineers in the Space Flight Operations Facility at NASA's Jet Propulsion Laboratory (JPL) made their last attempt to revive Opportunity Tuesday, to no avail." [Emphasis mine]
They also said, "The final transmission, sent via the 70-meter Mars Station antenna at NASA's Goldstone Deep Space Complex in California, ended a multifaceted, eight-month recovery strategy in an attempt to compel the rover to communicate."
It costs a lot of money to have NASA Deep Space Network (DSN) stations or a Mars orbiting spacecraft track a lander or rover. As long as a project is officially active, there is money provided to keep up the tracking. But as soon as NASA declares "Mission ended" that money dries up, so there is no money to pay the people who would calculate when and where the DSN or Mars orbiter should point their antennas, or to pay the people on the lander project who negotiate antenna time with the DSN or a Mars orbiter project, or to pay for any of several other such activities needed to make such monitoring happen.
As @kert said, at this point even if something did happen to wake up Opportunity, it would be highly unlikely anyone would be listening. They'd have to be pointing an antenna at the right place at the right time, and would have to be listening to the right frequency band. Each spacecraft at Mars is assigned a narrow frequency band that is not shared with the other spacecraft at Mars, so you couldn't "accidentally" receive an Opportunity signal while listening to another spacecraft.
I expect that without solar power to operate internal heaters and with depleted batteries, getting very cold damaged one or more components like the batteries, interconnection cables, RF components, etc. Due to contrasts in thermal expansion coefficients, solder joints can pop, IC packages can break and connections pop, all sorts of things. Coming into winter, which starts later in 2019 for Opportunity's location, without pre-orienting to a survival position and attitude, at least some of those will probably happen, maybe even all of them.
This points out a couple of the advantages of a radioisotope power source (RPS), like the one on Curiosity (which is a radioisotope thermoelectric generator, RTG): the supply of electric power is independent of the amount of sunlight it is receiving; and the waste heat from the RPS is more than sufficient to keep the rover's insides warm, and if the thermal system is designed properly can keep the rover warm without requiring electronics to be operating. They just cost a lot!.
One quibble with the NASA announcement: there is no "70-meter Mars Station antenna" at a DSN station. The 70-meter antennas at the DSN stations are not dedicated to the Mars program. They are used for whichever project and spacecraft needs them, such as the two Voyager spacecraft. The 70-meter antennas are too valuable a resource to have any of them dedicated to a single project, especially if they would sit idle when Mars isn't in the sky above them.