This is very difficult, and I think others will be along with wider advice for you, but I wanted to flag up one simple thing you can do.
Write a letter to your partner's doctor, explaining your concerns. say that you will be trying to persuade him to get an appointment, but in the meantime would like your concerns recorded - you can add 'please do not mention this letter if he does attend' if you want to. The doctor cannot actively do anything, but if your partner attends for another reason, they may ask certain questions or suggest certain tests because of what you have written.
I would also suggest (and forgive me if you have already tried this) that you find a support group for the families of alcoholics. Dementia is common in alcoholics. You could also go to the GP on your own account, to ask about support for yourself, and consider telling partner why.