If your ex-partner can no longer meet your maintenance payments either of you can apply to the court for permission to vary the relevant terms of the settlement.
Not every type of financial order can be varied, as it is intended that capital orders such as lump sums and property adjustment orders should allow both parties a level of certainty for their financial future.
An application to vary a financial order can be made on a number of grounds. The original order can be challenged on the basis of fraud, mistake, material non-disclosure or misrepresentation. This application would need to establish that the relevant order was made on the basis of a false pretence and that this premise substantially changes the nature of the order made. However for you to have a real chance of success the change to the nature of the order must be substantial.