Portability of Cloud applications

If an enterprise wants to migrate its applications from one cloud service provider (csp) to another , it could be a majoor issue. Similarly what happens when an enterprise has a major dispute on performance issues or commercial  matters with his CSP?  Can the CSP unilaterally switch off the enterprise application and stop further access?  If the CSP stops access how can he enterprise retrieve his data ?  Unless this is solved, why should any one use the cloud?