A lot of universities have (often not well publicized) programs to help you finish bachelor's degrees after you drop out and are gone for a few years. You can sometimes get credit for work experience or other things you've done and take all/most classes online.

I went through one myself and am currently working on my PhD. If you have a relevant career or just come off as pretty mature a master's program will be happy to have you even if there were issues in your undergrad, but very few institutions worth going to will admit you without a bachelor's of any kind and the circumstances would have to be something truly remarkable.