Yes, yes they DO need some sort of estate plan — or the lawyers, and possibly the government — will get some of the money they wanted you to receive!
First discuss their assets. If it’s a home, they likely have it in joint name. When one dies, the other becomes the sole owner — no will needed. BUT, if one is incapacitated (think stroke, dementia), the other joint tenant cannot sell the home unless he/she goes through a long,expensive process of declaring the other to be incapacitated.
Then when the survivor dies, if there is no will the house must go through the probate court– where it will be determined if you are indeed the ONLY heir. That could take months — and you’d have to pay a lawyer.
They probably have retirement plans naming each other as beneficiary. But you should be named as secondary beneficiary — no will needed. But if they don’t name you, the courts will again take over.
And other assets like stocks, personal items, etc will also go through the court process — while you wait,and pay attorneys! A simple will — or better yet a Revocable Living Trust (and remember to re-name property such as the home in the name of the trust) will save you time, money, and aggravation!