Unknown cost basis for stocks from old ESPP

I left a company in 2011 where I had stock through an ESPP. I've left it alone just filing the 1099-DIV every year until this year.

The problem:

My old employer was bought/had a merger and the company managing the stock was changed. Somehow through this transition they sold like .75 of my stock and I received a 1099-B because of the transaction. On this statement though there is no cost basis. My old employer doesn't know how to get this information.

The amount that it was sold for was not a lot. I'm in a pretty good financial situation to just eat the cost. Can I just put 0 as the cost basis and be done with it?