My advice is to find another contract!
Being responsible for the airframe in this manner just leaves you VERY exposed.
What sort of operation is it? What type of airframe? Where abouts?
These are questions that people would need to be able to assist you - but as I say - seriously think about it - it might just cost every cent that you have and every cent that you are likely to have for some time into the future if something goes wrong.
Even if the insurance company pays up if something goes wrong they won't pay immediately and the owner will, I am sure, want YOU to cover the losses until the insurance pays out.
Is there an excess?
It just seems to risky to me....