If booting freezes or you get stuck forever in the Windows Recovery Environment then you need to manually restore the automatically created backups for bootmgr and winload.exe.
The main goal is to copy "bootmgr~1" to "bootmgr" (at the root of some partition) and "winload~1.exe" to "winload.exe" (in \Windows\system32). After that you will be able to boot.
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