The NASA Mars Exploration Program is developing mission concepts for the capture and return of diverse geological and atmospheric samples from Mars to Earth. The first phase of a hypothetical multi-year sample-return campaign is the collection and caching of the samples; the second phase would center on the retrieval of the cached samples and launch of the cache into Mars' orbit, with the third phase being responsible for the capture of the orbiting sample(s) and their return to Earth. The second phase is known as the Sample Retrieval and Launch (SRL) concept, which would require a dedicated rover to retrieve the previously-cached samples for launch into Martian orbit, and subsequent return to Earth. Our contribution assesses the feasibility of conducting an extreme-terrain exploration mission in the extended-phase, following the launch of the cache into orbit. Our study leverages prior development of the MobileMAV concept, which uses Mars Science Laboratory (MSL)-based mobility to carry the Mars Ascent Vehicle (MAV)[1]. Our proposal is driven by the scientific value of exploring various challenging topographies such as recurring slope lineae (RSLs), craters, fissures, canyons, gullies, caves, and stratified terrain. These geologic features are expected to contain a wealth of scientific information that would greatly advance scientific understanding of dynamic processes in the Martian environment. The ability to operate on (and in) these challenging areas (and their environs) would also aid in the search for habitable environments, and significantly shorten the path to human-driven Martian exploration. The core contribution is an investigation of a trade space that would integrate a two-wheel, tethered rappelling rover (based on the Axel extreme-terrain rover [2]) into the mobileMAV concept, capturing the key benefits and risks to the overall mission. Although introducing new rover designs reduces our ability to leverage flight-tested heritage hardware, the possibility of dramatically extending the science capabilities — while simultaneously achieving the primary mission goal of delivering the MAV to the launch site — would be compelling. We present a conceptual design that is, to first-order, compatible with the existing MSL launch, cruise, and entry, descent and landing (EDL) baseline. We require minimal changes to the existing architecture to accommodate the rover and MAV payload. Although some challenges exist with respect to flown weight (greater than MSL) and available avionics payload (smaller than MSL), the required technological advances appear well within the projected arc of technology development, given the proposed mission concept timeline.