Installation from nothing : First win7 then linux-mint.
Win7 writes in MBR something to control boot and linux uses grub to control boot which will be able to boot windows.
Why not in the reverse order?
A complete re-installtion of win7 may over write ALL in MBR meaning the part that will call the actual grub configuration (in /boot or /etc/grub.d not sure...), therefore the repair of the linux booting is needed.
Result: grub boot first, if you choose "windows" then the machine will boot windows.

From this point. (A)

If linux system needs to re-install by totally erasing the linux part of the disk : Configure boot because after erasing the disk the grub (principle boot) now will encounter error and stocked.
Solution : boot the linux (which will be erased) with windows using EasyBCD.
{
1. Add New Entry
Type: Grub2
Name: [write the name of the system]
Drive: [the partition on which the current linux system is installed]

2. BCD Deployment
Use defaut and click "Wirte MBR"
}
After the step2, windows will be able to replace grub as the principle boot. Then after this, it won't be a problem with booting if we erase completely the linux system.

If from point (A), want to re-install windows ?
Maybe have to repair the linux booting after a complete windows re-installation.
But I tried ghost recovery. And it won't touch the MBR so this is an alternative.