It is possible to move applications from mainframes to Linux (or Unix or Windows) ... however, it is usually a long (5 to 8 years, often), expensive (as in millions of dollars) project. A former employer moved a system from a mainframe to Unix servers. It took several million (7 to 9 is the range I heard) dollars and multiple years, and the last I heard the end users consistently complained about how slow the response time was -- even though the system had been upgraded to 16 Unix servers from the original 4. Problems with such a migration include validating the business logic has been captured in the new system, response times, scaling up the system when needed, and so on.
I'veheard IBM licence are too expensive, and some society (more and more) decide to get ridof IBM services to go open source (linux, java, etc..)
If you look at the total cost of ownership, mainframe systems tend to compare favorably to Unix / Windows / Linux solutions but the specifics MUST be evaluated by each company as there may be special requirements that skew the ownership costs in one direction or another. For example, my former employer was spending about $750,000 on the mainframe -- and the server consolidation project for that year cost over $1,500,000.
You simply CANNOT say that "IBM license [sic] are too expensive" without doing a LOT of research in advance. My experience is that smaller mainframes are more easily replaced by a Linux/Unix/Windows (LUW) solution, but the larger mainframes will not be replaced by LUW systems or open systems any time in the next few years. IBM pretty consistently sells more mainframe capacity each year than the year before, so SOMEONE is buying mainframes.