Without the DAR file I don’t know of a way to reverse the process. The rendered folder is the end product of your menus, navigations, media etc. At lest you have all your media files and you can work from there. Here is what I would do.
1.Each one of those VOB files are MPEG2 files and you will need to convert them to a format Vegas can use. All of your menus are there as well so you will need to convert all of them. Vegas will read the VOB files but it will truncate them and make them unusable. There are many free programs out there that can help you do this. Or you can burn it to a DVD then rip it.
2.Once you have you have your files converted it is only a matter of rendering your new media in Vegas.
3.Depending on the type of Menus you created you can use those as well and import them back into Architect as a back ground media then overlay the added links you will need. If you need help with this let me know, I am leaving out a lot of details here as I do not know your level of experience.
4.You will have to redo all the navigation links, color sets, etc. There is no way that I know of to do what you are asking. There might be but I am not aware of it.
Hope this helps let me know if you are successful.
Joe