I’ve waxed poetic on FR (basically, run off at the mouth) about Martian missions and how they should go, so I won’t do that again. :’) Well, okay, since you insist...
The ISS will be deorbited (that is, pushed into a terminal trajectory into the Earth’s Pacific Ocean) once its useful life is done (that won’t be many more years, either). My view is, the Russian crap that’s part of the station should be removed for deorbit, and the remaining pieces relinked (slightly different order, plus some few additions as needed). Outboard stuff like the photovoltaics (with some additional ones) could be tethered to a leading mast (which would be one of the new parts) and at the opposite end would be a new booster.
Loaded with groceries and various other things, the ISS would be pushed up and away, on a slow trajectory to Mars, arriving at just the right time and path that little or no deceleration burn is needed to enter orbit. It would of course be renamed the MSS.
Remotely checked, it would become a destination for human missions to Mars. The process of getting to and from Mars is most of the mission’s time and risk, and Mars has no infrastructure.
The surface could be explored with rovers dropped in for the purpose, via direct and indirect links. Line of sight would be maintained between the station and two communication satellites to give nearly 100 percent coverage of the Martian surface. The rovers would be operated in real time by astronauts aboard the MSS.
One reason the lunar missions were a success was the development and practice of skills needed to do the jobs, step by step, beginning with Mercury and continuing with Gemini. Von Braun wanted to go to Mars, and stated in print that a single mission would require twelve Saturn V launches. Given how much has been spent on the STS flights over the last thirty years, twelve Saturn V launches looks pretty good right now.