After the succesfull ajax call set the datatype to local or clientSide, otherviese there is a now way tell the grid that from this point we should use local data.
There is a option for this. Look into the docs. Look at your events. Some of them must return [true,''] or [false,'']. Look if you request is valid. What they return?
You should check what you return from server. When you move from subgrid to grid as subgrid you should synchronoze the jsonRedear of the subgrid. The subgrid properties of the main grid in this case does not have sense.
Use onPaging event to store the selected rows in other variable array and the gridComplete event to select the previous if the array is not empty. Use setSelection for this purpose.
I'm not sure that this can be implemented easy. This is due the concept of jqGrid. Basically jqGrid uses the CSS property table-layout : fixed. There is another layout – table-layout: auto which do what you ask. Moreover when we have this, resizing columns will be a very hard job.
