How to save the current preferences in a dialog box so that its pre-filled.

I would create a txt-file next to the Script and read it (if it already exists) to populate the dialog and write it anew when the dialog is OK-ed. 

It may be crude but it might also suffice. 

////// read prefs file //////
function readPref (thePath) {
    if (File(thePath).exists == true) {
    var file = File(thePath);
    file.open("r");
    file.encoding= 'BINARY';
    var theText = file.read();
    file.close();
    return String(theText).split(",")
    }
    };
////// function to write a preference-file storing a text //////
function writePref (theArray, thePath) {
    try {
    var thePrefFile = new File(thePath);
    thePrefFile.open("w");
    thePrefFile.write(theArray.join(","));
    thePrefFile.close()
    }
    catch (e) {};
    };

Edit: 

/**/
var theFile = String($.fileName);
var thePath = theFile.slice(0, theFile.lastIndexOf(".")) + "_pref.txt";
if (File(thePath).exists == true) {var theArray = readPref (thePath)}
else {var theArray = ["aaa"]};

// remember the dialog modes
var saveDialogMode = app.displayDialogs;
app.displayDialogs = DialogModes.NO;


// Save the current preferences
var startRulerUnits = app.preferences.rulerUnits;
var startTypeUnits = app.preferences.typeUnits;
var startDisplayDialogs = app.displayDialogs;

// Set Photoshop to use pixels and display no dialogs
app.displayDialogs = DialogModes.NO;
app.preferences.rulerUnits = Units.PIXELS;
app.preferences.typeUnits = TypeUnits.PIXELS;

// DIALOG
// ======
var dialog = new Window("dialog");
dialog.text = "Auto Image Placement";
dialog.orientation = "column";
dialog.alignChildren = ["center", "top"];
dialog.spacing = 10;
dialog.margins = 16;

// TPANEL1
// =======
var tpanel1 = dialog.add("tabbedpanel", undefined, undefined, { name: "tpanel1" });
tpanel1.alignChildren = "fill";
tpanel1.preferredSize.width = 684;
tpanel1.margins = 0;

// TAB1
// ====
var tab1 = tpanel1.add("tab", undefined, undefined, { name: "tab1" });
tab1.text = "Single Story";
tab1.orientation = "column";
tab1.alignChildren = ["left", "top"];
tab1.spacing = 10;
tab1.margins = 10;

// MOCKUPGROUP
// ===========
var mockupGroup = tab1.add("panel", undefined, undefined, { name: "mockupGroup" });
mockupGroup.text = "Template File";
mockupGroup.preferredSize.width = 565;
mockupGroup.preferredSize.height = 64;
mockupGroup.orientation = "column";
mockupGroup.alignChildren = ["left", "top"];
mockupGroup.spacing = 10;
mockupGroup.margins = 10;

// GROUP1
// ======
var group1 = mockupGroup.add("group", undefined, { name: "group1" });
group1.orientation = "row";
group1.alignChildren = ["left", "center"];
group1.spacing = 10;
group1.margins = 0;


var mockupText = group1.add('edittext {properties: {name: "mockupText"}}');
mockupText.helpTip = "Select the template";
mockupText.preferredSize.width = 511;

var mockupButton = group1.add("button", undefined, undefined, { name: "mockupButton" });
mockupButton.text = "Select";
mockupButton.onClick = function () {
    var filter = "*.psd,*.tif,*.tiff";
    mockupFile = File.openDialog("Select Mockup File", filter);
    if (mockupFile) {
        mockupText.text = mockupFile.fsName;
    }
};


// INPUTGROUP
// ==========
var inputGroup = mockupGroup.add("panel", undefined, undefined, { name: "inputGroup" });
inputGroup.text = "";
inputGroup.preferredSize.width = 565;
inputGroup.preferredSize.height = 64;
inputGroup.orientation = "column";
inputGroup.alignChildren = ["left", "top"];
inputGroup.spacing = 10;
inputGroup.margins = 10;

// GROUP2
// ======
var group2 = inputGroup.add("group", undefined, { name: "group2" });
group2.orientation = "row";
group2.alignChildren = ["left", "center"];
group2.spacing = 10;
group2.margins = 0;

var inputInput = group2.add('edittext {properties: {name: "inputInput"}}');
inputInput.helpTip = "Select the input image folder ";
inputInput.preferredSize.width = 540;

var inputButton = group2.add("button", undefined, undefined, { name: "inputButton" });
inputButton.text = "Select";

inputButton.onClick = function () {
    var inputFolder = Folder.selectDialog("Select Input Images Folder");
    if (inputFolder) {
        inputInput.text = inputFolder.fsName;
    }
};


// OUTPUTGROUP
// ===========
var outputGroup = mockupGroup.add("panel", undefined, undefined, { name: "outputGroup" });
outputGroup.text = "Output Folder";
outputGroup.preferredSize.width = 565;
outputGroup.preferredSize.height = 64;
outputGroup.orientation = "column";
outputGroup.alignChildren = ["left", "top"];
outputGroup.spacing = 10;
outputGroup.margins = 10;

// GROUP3
// ======
var group3 = outputGroup.add("group", undefined, { name: "group3" });
group3.orientation = "row";
group3.alignChildren = ["left", "center"];
group3.spacing = 10;
group3.margins = 0;

var outputInput = group3.add('edittext {properties: {name: "outputInput"}}');
outputInput.text = theArray[0];
outputInput.helpTip = "Select an output folder";
outputInput.preferredSize.width = 540;

var outputButton = group3.add("button", undefined, undefined, { name: "outputButton" });
outputButton.text = "Select";
outputButton.onClick = function () {
    var outputFolder = Folder.selectDialog("Select Output Folder");
    if (outputFolder) {
        outputInput.text = outputFolder.fsName;
    }
};

// GROUP4
// ======
var group4 = tab1.add("group", undefined, { name: "group4" });
group4.preferredSize.width = 660;
group4.orientation = "row";
group4.alignChildren = ["center", "center"];
group4.spacing = 14;
group4.margins = 0;

var okButton = group4.add("button", undefined, undefined, { name: "okButton" });
okButton.text = "Create";

var cancelButton = group4.add("button", undefined, undefined, { name: "cancelButton" });
cancelButton.text = "Cancel";
cancelButton.onClick = function () {
    dialog.close();
};


okButton.onClick = function () {



    var outputPath1 = outputInput.text;
    var mockupPath1 = mockupText.text;
    var inputPath1 = inputInput.text;
    writePref ([outputPath1, mockupPath1, inputPath1], thePath);

    dialog.close();
};


dialog.show();

////// read prefs file //////
function readPref (thePath) {
    if (File(thePath).exists == true) {
    var file = File(thePath);
    file.open("r");
    file.encoding= 'BINARY';
    var theText = file.read();
    file.close();
    return String(theText).split(",")
    }
    };
////// function to write a preference-file storing a text //////
function writePref (theArray, thePath) {
    try {
    var thePrefFile = new File(thePath);
    thePrefFile.open("w");
    thePrefFile.write(theArray.join(","));
    thePrefFile.close()
    }
    catch (e) {};
    };