I owned a co-op once. Sold it 3 years ago and now "unfortunately" rent. I would suggest posting this question to "Home Buying" boards. Other than that maybe you could call the management office at the co-op and explain this to them. Maybe can direct you.

I live in a co-op that's self-managed, and I know that since all the work is done by the residents of the building, sometimes stuff takes a little while.

Contact the co-op board and tell them that you need to get moving, and what can they do? Also alert your seller to your potential problem.

And check w/ your lawyer--Does your contract have some sort of time clause, so can you cancel the entire contract if the delay makes you lose your rate lock? This would be a wise clause no matter what sort of home you're buying, but it is especially important w/ co-ops because there are a LOT more moving parts. Not that this helps you now.

And of course check w/ your lender to see what sort of new rate you could get--it may not make a huge difference, and that would influence how worried you feel, and what sort of resolution you push for.