The "rescue partition" holds Microsoft files to recover the system in event of certain software failures. Your data is your own problem as far as Microsoft are concerned.
I seem to recall reading somewhere that Windows 10 has been set up to insist on being the only operating system on a computer. Microsoft don't like the idea of people being able to boot into multiple operating systems other than their current version of Windows. The days of selecting which operating system to boot into when the computer starts up are coming to an end.
From a security point of view, that makes sense. It also simplifies support if there is only a single unified operating system installed on multiple platforms, PC, tablets and phones. So kind of a cost cutting measure in a way.
To use a motoring analogy, you can drive any model car you want, but even if compatible parts are fitted, the manufacturers warrantee is void if service is not carried out by their agents using their branded parts. Tyres and windscreen wipers can be swapped, everything else must be done through official channels. Engine upgrades or tuning of any sort immediately voids all guarantees.
There are work arounds, but you do need a decent level of technical knowledge and a bit of luck to get it all set up successfully. You are completely on your own with that type of setup if something stops working. Microsoft will refuse support and High Street computer shops haven't got a clue other than to reset the system back to how it was when the computer was purchased.
They all hide behind the licensing agreements that you agreed to before your computer would even boot up.