Robots could certainly be used for further exploration of Mars, and they should be the primary means for exploration. They could engage in all sorts of projects, including a search for life forms, or at least evidence that life once existed on the red planet. The equipment needed to find definitive evidence of life is much more sophisticated and much more compact than it was in years past. Robots have big advantages over sending humans.
Sending robots is cheaper. Machines do not need all the life support equipment and material that humans require. No need for oxygen, water, and food in sufficient quantity for a round trip (we do want to bring them back if we send humans to Mars, right?). Which brings up another big advantage: robots only go one way. There is no reason to try to bring them back. The equipment is cheaper, the flight is much cheaper, and the number of people required to plan and operate the mission is much less, so that reduces costs as well.
Robots do not get sick or tired, and they never misunderstand orders. If they depend on solar energy for operation then mostly they can only operate during the day, but the robot does not care. If it has energy to run during the night it will do so. Robots are never too hungry or thirsty or bored to do their jobs.
If some kind of disaster happens or if it is just a matter of an equipment malfunction, the worst that can happen is lost contact with the robot or it ceases to function. If humans are sent, any serious problem could result in loss of life. Depending on where Mars and the Earth are in relation to each other, they will be between 55 million kilometers (about 34 million miles) and 400 million kilometers (about 249 million miles) away. Under optimal conditions, it could take two years for a rescue mission to arrive.
Robots can easily take soil samples and analyze them for specific traces that indicate life. They can also crush small rocks and examine them. They can operate a drill and remove samples from underground for analysis. The technical and engineering knowledge to send a swarm of robots to Mars already exists. If we insist on continuing to explore Mars, robots are definitely the most practical way to do it.
This is all really about the wrong planet, though. Mars may show some traces of life, but it is almost certainly long gone. Scientists might gain some knowledge of early forms of life and possibly something about how it arose and how it has spread into other locations. On the other hand, it is also possible that Mars is dead and has always been dead. In either case, the benefits of exploring Mars are very limited. It is not fit for human habitation and it would take some serious terraforming (earth-shaping) to make it suitable for long-term occupation. Venus, on the other hand, could be made into another home for our species. The focus, in terms of effort and funds, should be shifted to Venus.