With no dependents, 7 years from FI, and a policy from your employer, it doesn't seem necessary to buy disability insurance. Take a look at what your employer's policy offers, and check out your last Social Security statement to see if you could still FI in 7 years while making ends meet on your employer's policy and Social Security Disability.
If you can't make ends meet there, and it would trash your FI goals, making you not able to support yourself in the long run, then a disability policy might be worth it. To lower your premiums, you can get a policy with a waiting period ("Elimination Period"), because your employer's policy will kick in to support you while you wait for benefits to kick in.