IMHO designing a system that would enable a pretty good odds of coming back would be at least an order of magnitude more expensive than a similarly reliable one way system.
Think of all the additional R&D and engineering difficulties involved in keeping a human alive long enough to get there, do something there come back and survive.
More to the point, what's the cost of a Moon base - where a return and even a rescue is feasible - AND a one-way extensive robotic exploration of Mars. It just seems an overly dramatic waste (there will be no shortage of people willing to go) to send people to die on Mars when we can get the same off-Earth habitation expertise and Mars scientific data for the same price or cheaper.
The thing with Mars is, once you're on the surface, you can manufacture fuel for the return trip in-situ. Dr Robert Zubrin covers this in his Mars Direct mission blueprint.
And you get oxygen to breathe for free! The Mars Direct plan calls for the initial deployment of an unmanned mission to set up a fuel station on the surface - then unmanned missions to cache supplies there - and only when you have enough stuff pre-deployed for the return trip and/or a permanent presence, send humans.
The moon may be closer, but until you have a working fusion reactor, there's not much you can usefully do there in terms of resource extraction.
IMHO designing a system that would enable a pretty good odds of coming back would be at least an order of magnitude more expensive than a similarly reliable one way system.
Think of all the additional R&D and engineering difficulties involved in keeping a human alive long enough to get there, do something there come back and survive.