The legal answer is 'no' and the remedy is to file an application in court asking for extension. The practical answer is also no and unless you can show something other yhan diminished income, a court will not disturb the agreement and you'll be out of luck.
If your disability occurred after the divorce, that may be a change of circumstances. Medicare is medical insurance, not a cash payment to you. The standard of proof would depend on whether you originally had a consent order or you agreed to the amount by stipulation. Either way, if you are now disabled, you may qualify for additional spousal support.
When you get closer to May of 2015, you should file a petition in the Family Court to modify the order of maintenance. Bring with you, your proof of disability. Maybe you will be able to work something out with your ex-husband at that time. It can't hurt to try.
Advice on this forum is for informational purposes only and should never be mistaken as a substitution for legal advice. Answering a question does not create an attorney client relationship. If you need legal advice, you should consult or retain legal counsel.
My esteemed colleague is correct. As a former judge, I never extended alimony/maintenance.
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice. Mr. Leroi answers questions on Avvo because he strongly believes in public service from his years as a judge, magistrate, and prosecutor. If you need to ask any follow up questions because my answer did not fully address your question, feel free to call Chris or post an additional question. Thank you.