There is no legal issue if an employee is leaving before the period pre fixed. But if your Certified Standing Orders insists a three months' notice period, then you can ask the employee to serve the notice period or pay salary in lieu of notice. But without any such clause about notice period and payment in lieu of notice, you cannot insist an employee to serve a notice period if he is a worker/ employee coming under the scope of Industrial Disputes Act. Obviously, an employee who has no reportee under him or an employee by whatever designation he is called has no authority to sanction leave of his subordinates, appraise the performance of his subordinates or initiate disciplinary action against subordinates is a worker who will get the protection of ID Act. Therefore, please insist for notice period after ensuring that he is not a workman but a manager by functions.
You can demand a training cost from the employee but the cost should be evidenced as cost of training for the employee concerned. It should not include a general costs of training. Normally, for a fixed term contract of 18 months, what would be the training and what would be the training period therein? If the idea is to train the employee and use his skills, then a period of 18 months is very less. Suppose out of 18 months, the training was for 6 months, then naturally, the employer would expect that the employee should be with him at least for a reasonable period, say five years or three years. Similarly, non one would spend huge amounts by way of training if the return is expected only for a very small period, say one year. These are some reasoning about training costs and its recovery. Anyway that depend on the actual scenario, but I would say that if the amount involved in training the particular employee is quantifiable, then you can demand it from the employee.