The sync button isn’t hidden. They have removed it. There are numerous comments on the forum requesting it back. No matter how good they think they can make the sync, and v10 is definitely not there yet, I think we should always have a manual sync option.
If this is a note that you have been working on for ~2 years then Evernote will have note history for it. If you sign up for premium for one month then you will have access to note history and should be able to grab the last version saved.
That is correct. EN will not allow a local notebook to be used as a default. You are required to have at least one synchronized notebook.
I use mainly local notebooks myself but have one sync'd notebook named inbox that I use for collecting emails to EN or webclips. I check that daily and then move the notes from there as needed.
I found the older post that I was thinking of. I stand corrected, the upgrade path is no longer supported by Evernote customer support, but here are the details. Use at your own risk and please backup your data first before trying.
EverNote v2.3: https://dl.dropboxusercontent.com/u/12760413/EverNote2.zip-- this is a patched executable which can coexist with modern versions of Evernote.
Evernote 3.1: https://dl.dropboxusercontent.com/u/12760413/Evernote_18.104.22.1685.exe-- this is the last Evernote version that could import EverNote 2.x databases.
EN2Export: https://dl.dropboxusercontent.com/u/12760413/EN2Export.zip-- stand alone utility that converts EverNote 2.x databases (.enb) to modern EverNote database (.exb). Currently it converts HTML notes only, all other EN2 note types are skipped. I may add support for other formats if someone needs it.