move the file to another directory, rename it back messages.tbb
Start TB
Tools -> Import -> From TB message base

This will offer you the best chance to rescue something.

Since your inbox was 30MB big, I suppose you might not have compressed it often enough, I suggest you might decide to turn on 'Compress on exit' and don't save important mail in the |Inbox, just to avoid troubles in the future. Here's why:

TB manages your messages as a database or to be more precisely: stores
them in a database. This database is organized per folder. Each folder
has a messages.tbb and a messages.tbi file.
The real messages are stored in the messages.tbb (The Bat Base) and to
shorten the access time to the messages additional info is stored in
the messages.tbi (The Bat Index). This additional info can be a flag
you've set to the message, the info whether you've replied to it or
whether you deleted the message.
Deleted? you'll say. Yes. When you delete a message, TB flags the
message as deleted in the index file, but leaves it in the actual
message base. That's because setting a bit in the index is faster than
rewriting the full messages.tbb. In the folder menu you'll see an
option 'browse deleted messages' where you can view and undelete your
deleted messages.
Will TB never delete messages from the messages.tbb? Yes, it can do
that, but that's called 'compressing', you'll see an option 'compress'
in the folder menu. This means that TB will rewrite both your .tbb and
.tbi files and what's deleted is lost 'forever and ever'. You can also
compress folders automatically on closing TB. Since version 1.60 you
can set this for all folders in the account settings. And in the
folder properties you can do this per folder (compress on exit).
TB has also a 'purge'option. In the folder properties you can setup a
maximum number of messages or a maximum age for the messages in that
folder.  That's called purging. Purging is the same as deleting, the
message is flagged as deleted, until you compress the folder. Purging
can be done automatically and manually (from the folder menu)
Note that moving a folder (manual or by filter) will create the
message in the new folder and mark it as deleted in the source folder.
Now you'll see why it is important to compress your folders,
especially those that are seeing lots of messages being deleted or
moved. (Your inbox is an example of them.)