The Ubuntu should survive unless the grub menu is destroyed and/or the wubi
partition.

How would you boot a MS folder???

There is a grub that is installed that allows you to do that. Check out
http://wubi-installer.org/ for more info.

That does not tell you that Ubutu installed into a widows folder will
open independent of a windows system, it does not install grub.

Wubi is Safe

You keep Windows as it is, Wubi only adds an extra option to boot into
Ubuntu. Wubi does not require you to modify the partitions of your PC,
or to use a different bootloader, and does not install special drivers.
It works just like any other application. Wubi is spyware and malware
free, and being open source, anyone can verify that.

If Windows dies,the Linux installed under Wubi will not be accessible.
Wubi install makes it similar to any other Windows program.

Of course it depends what you mean by die. Wubi places it in a folder of
the Windows system so he cannot use it if his windows does not open. He
needs to use a dual boot by partition or separate drive.

Not necessarily.

Wubi relies on Windows to create it, but not to run it. As long as the files are
intact and the Windows bootloader still exits, then Wubi based Ubuntu should
still boot. It is mounted as a drive and then run just like a normal one. The
loopback information is in the Windows bootloader file. The actual Ubuntu files
are inside the image file in c:\ubuntu.