Luckily, I made that Rhythm node. 
And it is long retired, so your version is WAAAAY old BTW.
That being said, it sounds like you want to return true or false depending on the Yes/No selection. Here is how to do that.
The python code in action:
and the actual code for copy pasta:
import clr
clr.AddReference("RevitAPIUI")
from Autodesk.Revit.UI import *
dialogContent = "You are about to delete all Fabrication Pipework content from the model. Are you sure?"
buttons = TaskDialogCommonButtons.Yes | TaskDialogCommonButtons.No
#assigning this to a dialog result variable allows us to check what the user selected
dialogResult = TaskDialog.Show('Delete all MEP',dialogContent,buttons)
#define a return value parameter for use as an output
returnValue = False;
#if the user clicks yes, return true to continue
if dialogResult == TaskDialogResult.Yes:
returnValue = True
OUT = returnValue