I've just been through the same thing. This is how our accountant handled it:

In the year you investment becomes a total loss (i.e. bankruptcy), you can write-off your remaining basis (including any passive loss carryover from previous years). However, your investment probably breaks down into 2 pieces. Which means the loss has to be taken in 2 places on your return.

The non-syndication costs (i.e. cost of creating the comodity your partnership was selling) can be deducted from your ordinary income, thus lowering your AGI. This is usually the lion's share of the investment.

The syndication costs (i.e. commisions paid to the salesman that sold you the investment) cannot be deducted from ordinary income (of this our accountant was sure), but they can be taken as a capital loss on schedule D. (However, our accountant said this is a grey area with the IRS)

We did get a final K-1 (and need to chip in to pay for the accountant), so I'm not sure what the rules are if you didn't get that final K-1. Sounds like you want to talk to a tax professional.

Mark