Magic Mountain will remain a theme park — not converted into a housing development or retail complex — if Six Flags Inc. Chief Executive Mark Shapiro has anything to do with it. Shapiro told investors Tuesday that the company expected to decide by the end of the year whether it would sell Magic Mountain and several other properties to reduce its $2.2-billion debt. He said all the parks would keep operating for the foreseeable future and wouldn't be sold for their real estate value.