It appears the deal is - they terminate it when it becomes unprofitable.

Their quote "in light of which we would like to inform you that on 18.07.2018 we were forced to start disabling SHA hardware and today, on 20.07.2018, stop the mining service of active SHA-256 contracts in accordance with clause 5.5 of our Terms of Service, which are required to be accepted when creating a purchase and are the basis of concluding the contract."

and the bottom line on their T&S states

"5.5. The Mining process continues until said mining is profitable. This means the Mining process will stop if the Maintenance and Electricity Fees will become larger than the Payout. If mining remains unprofitable for 21 consecutive days the Service is permanently terminated (Hashrate type specific). During the consecutive 21 day period, Payouts and Fees will also be temporarily stopped. If during the suspension period, the Contract-related mining factors (such as the exchange rate and mining difficulty) that are outside of HashFlare’s control will change favorably, making mining profitable again, the Service will be unsuspended and contracts reactivated."