Windows 10 Upgrade - All programs gone

I just got suckered into upgrading from Windows7 to Windows10 (clicking the "download" instead of the "install" button still forces you into an upgrade within a week with no way to cancel). The update itself took 2-3h and it seems to work, at least the desktop comes back up and stuff. However, pretty much all the installed programs are gone. The only thing left are old copies of Word & Excel 2003 and those fail to start on Windows10. Nothing in the startmenu or on desktop. This does not seem to be the intended behaviour, does it? Quick Internet search at least didn't bring up a lot of complaining. So what's going on here?
Now the programs are still in C:\Windows.old, but I assume there is no way to make them work in Windows10 without a proper reinstall.
So what are my options now to get the system back into working conditions? Reinstalling all the apps is something I'd like to avoid. So that leaves the Windows7 downgrade option, which is bound to a timelimit of a month before potential dataloss.
Does the Windows7 downgrade work without issues? Or will I go from broken Windows10 to broken Windows7? Is it possible to update back from a downgraded Windows7 to Windows10 at a later point? And how long will the downgrade take?

I still have no idea why none of the applications got carried over from Windows7 to Windows10, among them lots of really standard stuff Audacity, IrfanView, iTunes, etc. However I did now do a downgrade from Windows10 back to Windows7 and that worked mostly as expected. Took around 20min and Windows7 booted back up normal. Only issue I could see so far is that all the pinned applications in the task bar stopped working and had to be repinned, but otherwise I haven't found any issues yet.


The Windows10 nag screen came right back after the downgrade, so I guess future upgrades back to Windows10 are still possible.