If you decide to take a mortgage protection insurance plan you would normally pay for it on a monthly basis. The premium per month is decided at the outset and more often than not this is a reviewable premium. A reviewable premium means that the price can be looked at by the insurance company and they could decide to increase the premium, keep it the same or reduce it for the next year.
The insurance is paid for in advance and when you pay the premiums they are done for the month up and coming. If you maintain payments of the premiums then the contract will continue, if you stop making payments on the plan then the policy will cease. You normally are not tied into any form of contracts.