The company can facilitate the arrival of employee and make the beginning easier for employee in many ways. A good welcome starts with flight to the destination, arranged transportation to the first accommodation from the airport and providing help to arrive easily to the workplace on the first day. Usually foreigners need to deal with the local officials to get local id number, social security number ETC. Dealing with the officials can be difficult if you do not speak the local language therefore providing tutor who can help with bureaucracy is a big help.
Warm welcome does not make employees stay for the long term. If the company wants the people hired from abroad to stay it is essential to facilitate their adaptation to the new country. I have considered the factors that make employees stay working abroad long term. The company can offer accommodation as a part of the work contract. Especially sharing a flat with or living in close proximity with other new comers makes forming social circles easier. Also organizing activities during the work day and after work day facilitates socializing. Learning the local language facilitates the adaptation and therefore offering language lessons for the employees is a good idea. I think that companies should hope their single employees to find a partner to make them stay for the long term.
After all the big reason why many people keep working is to pay their mortgage. Paying mortgage ties the employee to work life for many years. The barrier to take mortgage abroad is higher than in your home country therefore the mortgage is not tying foreign employees similar way as many of the local employees. It is hard to imagine foreigners taking a mortgage abroad unless they have decided to form a family.