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answers:
Davros say: Depends on political will. With the US' present government you'll be lucky if there is still much of a space agency left by the end of it. Not sure how it feels to people on the ground in the US but to us outsiders it looks like the US has lost it's damned mind and turned full on anti-science denialist. America seems more keen today to spend billions building shiny new megachurches than spend it on exploration.
Although they already have or could develop the technology plus have the existing knowledge base to do it, no other national space agency has the finances to mount a Mars expedition. Not one that may meet your 50 year time frame anyway. Who knows though as that's a long time in politics.
Outside of the US I don't think anyone is even talking about it, I guess it's always been assumed that this is NASA's patch and they've focused their efforts elsewhere. A combined effort between agencies could see a Mars mission take form but given the continuing legal and bureaucratic nightmare on projects like the ISS, such collaborations can be off-putting. Huge amounts of budget go not on the hardware or the astronauts, but on the attendant army of lawyers, accountants, political representatives, oversight committees, administrators and interpreters. I'm also reminded of the punishing years of delays and wrangling over ITER, another mammoth international science collaboration. International cooperation is sadly too easily prey to pen pushers and may actually serve to cripple a mammoth project rather than promote it.
There are some wildcards. The first is private enterprise, with Elon Musk especially being a vocal proponent for a Mars expedition. Although undoubtedly the greatest advert for SpaceX hardware is the demonstration of a Mars mission, I really don't readily see how even Elon's vast fortune and company resources could pull it off. Mind you, many wrote SpaceX off as a doomed pie-in-the-sky venture and they were wrong.