Parties to a lawsuit generally have an absolute right to nonsuit (dismiss) their own claims for relief at any time during the litigation until they have introduced all evidence other than rebuttal evidence at trial.
In Missouri, parties to a lawsuit do indeed have the right to voluntarily dismiss their claims, which is often referred to as a 'nonsuit.' According to Missouri Rule of Civil Procedure 67.01, a plaintiff may dismiss their case without prejudice by filing a notice of dismissal at any time before the plaintiff rests their case at trial. This means the plaintiff can dismiss their claim any time before they have finished presenting their main evidence, but not after they have started to present rebuttal evidence or after the case has been submitted to the jury. If a case is dismissed without prejudice, the plaintiff may be able to bring the claim again at a later date. However, there are limitations and specific conditions under which this right can be exercised, and if a plaintiff has previously dismissed a claim, a subsequent dismissal may be with prejudice, barring the plaintiff from bringing the claim again.