There are two sides to this. The first is that mortgage insurance decreases in value at the same rate that the mortgage balance does, this can be viewed as a positive by many because they're not over insuring themselves. The reverse to this is that mortgage insurance is dollar for dollar more expensive then a 20 year term in most cases, so if you buy a 20 year term for $250,000 it should for all intensive purposes be less then a mortgage insurance policy that will start off at $250,000 and slowly decrease overtime, but you could be overinsuring yourself.
I guess you'd want to look at your total insurance to make a decision. If you have a lot of other insurance (enough for the surviving family member(s) to replace the deceased's income for 10 years), then mortgage insurance may be right, but if you are currently at minimum with insurance, you should probably look to reevaluate your whole insurance/investment portfolio.
