Coming in late (sorry), this is probably less helpful, but for future reference:
First, back up the project, whatever state it it’s in. No sense risking losing anything further, especially since you know all the writing is there, just not showing up properly. It does sound like an older version of the .scrivx file overwrote your newer one, which means that in Dropbox it’s going to show up as a previous state, not as deleted, so you’d want to roll back that file. Unless you’re familiar with XML, it’s not going to be the easiest thing to tell just by looking at the file itself whether the older version contains all the correct edits, but theoretically once you’ve got a full backup safe and secure somewhere else, you can test by restoring the previous version in dropbox and then checking that. The problem is that it may have been more than just the .scrivx file that didn’t finish updating, so it’s likely you have other files that are out of sync which you just didn’t notice. Some of these won’t matter, and Scrivener will just create new versions anyway; some of them, like your text files, will matter, and you’ll want to make sure that each of your text files really is the most recently edited version. You’ll also want to check for any “conflicted” files in the project and then ascertain which of the versions (regular or conflicted) is the one you want to keep.
All in all it can be a little messy, but given that Dropbox does save 30 days of revision history, you can usually find all the pieces.
If it’s just the .scrivx that’s the critically goofed one, you can restore your text into the project by just hitting “new document” a bunch of times in the binder. Each of these will be magically populated with the missing text, so just keep doing that until you’ve restored all your documents and new ones are coming up blank. You’ll have to re-enter the title and meta-data and reorganize them in the binder, but they’ll be there. (Scrivener just creates the text files and links to them in the .scrivx file using incrementing numbers, so when you take an older version of the .scrivx and add new documents, it adds links to numbers that already exist in the project–thus linking the new binder item to the existing document.) So long as all your text is right, this is probably the simplest way to restore the project, even though it does mean redoing your meta-data. (Synopses and notes will be preserved by this method.)
Happily, with the advent of 1.0, Scrivener will also make automatic backups every time you close your project. You can adjust these settings under the “Backup” tap of Tools>Options… but just with these default settings, what would’ve happened in your case is that when you closed the project on the work computer, you’d get a backed up copy of the project. After you discovered the snafu with the laptop and files getting out of sync, you could just restore the entire project from that backup by removing the current corrupt one from Dropbox and putting a fresh copy from the backup in its place. So hopefully, even if this problem does happen to you again, restoring quickly and safely will be much easier.