Mars lost its atmosphere on a geological time scale. You just need to raise the average temperature 5C to create a runaway greenhouse effect (and that gas release from the polar regions would far outpace the solar winds stripping atmosphere away and once it leveled off would take millions of years to get back to the state it is in now).
The very thin atmosphere it has now, will take another 2 billion years or so to be stripped away entirely.
Water escapes from Mars' atmosphere over periods of millions of years. It's unlikely that domes would help very much. They'd crumble long before they protected any meaningful amounts of water.
The very thin atmosphere it has now, will take another 2 billion years or so to be stripped away entirely.