However, the defendant rejects any deals by pleading not guilty, so it might result in a more severe sentence.

A bit tangential, but: In any criminal case (goes for civil, too, but with different terminology), the accused should always plead "not guilty" at arraignment. You can change your not guilty plea to guilty later on, if the prosecution offers a plea deal, or if some other set of circumstances make that plea your best choice. If and when you plead guilty, that's it, all over, move on to sentencing.

Further down this rabbit trail, if you arrange it with the prosecution, you can plead "no contest," which is a guilty plea that cannot be used against you in a later civil case. The plea itself does not make you civilly liable. In 47 states (exceptions: Indiana, New Jersey, and Michigan), you can submit an Alford plea. This plea is "I still proclaim innocence, but I agree that the State case is strong enough to convict me, and I do not have a sufficient defense." Such a plea is allowed when the plea deal offers an escape from a more severe sentence, as in life in prison vs. capital punishment, making the plea "in the best interest" of the accused.