Oh man, somehow I missed your post here, sorry. Yes, you could absolutely put it back. The only major difference between doing iTunes Match and just doing things the old way is that with iTunes Match everything is done wirelessly. So if you were going to go on vacation, you'd download all the music you wanted via your wifi connection onto the iPod and when you got back you could just delete it from the iPod itself. While you're connected to wifi on vacation though, anything you DIDN'T download would be viewable in the iPod's music player and you could just listen to it via the "cloud" (over the Internet) or download it to the iPod also. Once you're off wifi though, the stuff not on your iPod goes away from what you can see.
This is only with iTunes Match though. If you are not subscribed to that you're only going to get what you have in your music app. You'll be able to switch over to the iTunes Store app and purchase more music, or see previously purchased items that you can download from iTunes, but other stuff in your library that you didn't buy from iTunes will not be in there.
e: this is what the various menus will look like.
iTunes Store Purchased Music area
Download a whole album/single/EP from there
Download individual tracks (click on the title of the album to get here)
Music App with all my music showing
Music App with just what is actually on the phone showing
An undownloaded single
After downloading
Deleting a track (swipe the track)
Appearance after the track is gone