Well, first of all an enquiry was required to be conducted. It is well known that our behaviour depends on circumstances and there are certain trigers, emotions which controls our behaviour. If the employee mis-behaviour only once, then, a warning was sufficient but if the employee was habitual then his termination was according to law.
Furhter, if your company has lost the customer, then, you can take the stringent actions. It could be possible that your customer misbehaved first and your employee just retaliated.
It is advisable to provide all the dues to your employee and help him to find a new job. Try to make him emotional intelligent. If possible, try to re-appoint him, provide him training that How to deal with difficult people. What ever we do in our life, we just deal with people. Our teacher teaches us, Banker do advise us in financial matters, Bus driver drives bus for us, washermen washes cloth for us, Army people do secure our country. Now, do you expect that whether, an individual can perform all the jobs alone. 'NO'. Therefore, being human, you should understand this fact and help others.
Litigation do not solve any purpose, it will be the wastage of time, money and trust. It also seems that our managers are not well equiped to handle such scenarios as they lack the basic principle of management.
One question from my side that Whether in your organisation training on behaviour aspects are being conducted or not?
Please revert.