There are cases when people are found to have three kidneys, so in order to improve their material condition and give a positive answer to your question, these people can live without two kidneys.
Technically possible, albeit difficult. Initially, nature established that for a comfortable existence a person needs two kidneys, but in order to survive, one is enough. There are even cases when a person is initially born with one kidney, and does not experience any problems in this regard. As a rule, people left completely without kidneys are forced to constantly undergo a hemodialysis procedure: blood purification. This is such a hefty bandura that pumps blood, cleans it and pumps it back (of course, not all at once). The procedure is long, exhausting, unpleasant and expensive. Therefore, it would probably be more correct to say that you can exist without kidneys, but life is extremely difficult.