Res Ipsa Loquitur - is a rule of evidence - in cases where the act of the person is so gross and negligent on the face of it - it speaks for itself that the person was negligent. Here leaving a mop inside the abdomen of Patient is something that no reasonable man would do, he failed to take even observe minimum reasonable care. Here the patient need not prove the traditional requirements of tort of negligence - 1) Duty to take care 2) Breach 3) Resulting Damage. These need not be proved. The presumption of negligence is attracted u/s 114 IEA. Now the burden to disprove negligence would fall on the doctor.
As regards criminal liability it is always there as sridhar said - in 304A in cases of Death and in 337/338 in case of hurt caused. Both are attracted. As in cases of negligence recklessness is the mens rea - the mental condition. Recklessness coupled with actus reus that is act of leaving mop inside the abdomen - would attribute liability on him. An attitude of mental indifference to obvious risk.
Civil Liability is always there. Exemplary damages to be awarded.