Yes I think you will lose the deposit. Basically part of the deposit is the insurance on the holiday and you are claiming on the insurance by cancelling. Most insurance policies have an excess i.e. you pay the first X amount so that will be the other portion you don't get back.
I would check the contract as to reasons allowed for cancellation - you may need supporting evidence.
Deposit normally non-refundable and a scale of charges against the total cost kicks in on a fixed timescale, increasing as departure date approaches, so check the Terms adn Conditions. Hopefully it will be just the £200 now but if you paid a low cost Travel Agent's offer deposit there may yet be more due if that is less than the Tour Operator's norm, sorry.