Sorry, I still dont get the whole picture of why this is so important for your plugin.
When you say,
"Once i closed, autocad exception dialog, Autocad is getting enabled but is should not enable"
Unhandled exceptions in plugins should not ideally cause AutoCAD to hang, so why is that you expect that AutoCAD should not enable again ?
You plugin should gracefully handle all the exceptions including a catch-all for System.Exception and take appropriate action without passing them on to AutoCAD. I dont think the behavior of AutoCAD to react to those unhandled exceptions from plugins can be configured.