Actually.. Here is one way, if you resize smaller than what the window is, it will snap back to default... I prefer to have it stop while resizing. I am going to mess around with it some more. I took the GUICtrlSetResizing() help file and edited it a little to show. Also, I used $GUI_EVENT_MOUSEMOVE instead of $GUI_EVENT_RESIZED because it has a faster response.
#include <GUIConstants.au3>
Opt("GUICoordMode", 2)
$nWindow = GUICreate ("My InputBox",190,114,-1,-1,$WS_SIZEBOX+$WS_SYSMENU); start the definition
GUISetIcon ("Eiffel Tower.ico")
GUISetFont (8,-1,"Arial")
GUICtrlCreateLabel ("Prompt", 8,7); add prompt info
GUICtrlSetResizing (-1,$GUI_DOCKLEFT+$GUI_DOCKTOP)
$nEdit = GUICtrlCreateInput ("Default", -1,3,175,20,$ES_PASSWORD); add the input area
GUICtrlSetState ($nEdit,$GUI_FOCUS)
GUICtrlSetResizing ($nEdit,$GUI_DOCKBOTTOM+$GUI_DOCKHEIGHT)
$nOk = GUICtrlCreateButton ("OK",-1,3,75,24); add the button that will close the GUI
GUICtrlSetResizing ($nOk,$GUI_DOCKBOTTOM+$GUI_DOCKSIZE+$GUI_DOCKVCENTER)
$nCancel = GUICtrlCreateButton ("Annuler", 25,-1); add the button that will close the GUI
GUICtrlSetResizing ($nCancel,$GUI_DOCKBOTTOM+$GUI_DOCKSIZE+$GUI_DOCKVCENTER)
GUISetState () ; to display the GUI
; Run the GUI until the dialog is closed
While 1
$msg = GUIGetMsg()
If $msg = $GUI_EVENT_CLOSE Then
ExitLoop
ElseIf $msg = $GUI_EVENT_MOUSEMOVE Then
$WinPos = WinGetPos($nWindow, "")
If $WinPos[2] < 190 Then
WinMove($nWindow, "", $WinPos[0], $WinPos[1], 190, $WinPos[3])
EndIf
If $WinPos[3] < 114 Then
WinMove($nWindow, "", $WinPos[0], $WinPos[1], $WinPos[2], 114)
EndIf
EndIf
Wend