I'd say - finish. A diploma is not necessary to be successful in life or to provide for your needs. But later in life you will compare yourself with others, your colleagues, your friends, and you might feel inferior, unfishied. Something will be missing, especially that you are at the end of the road, you're almost done.

The things you talk about are quite ambitious. Let's make a comparison with filmmaking world. If you are about to graduate from a film school, you are not supposed to make your first movie as good as some of the Old Masterpieces, or a big budget Holywood movie. You are supposed to make a soap opera episode - just get things simple and right - correct shots, correct lighting, well paced, clearly structured plot. And so should be the graduation work you are facing now.

And finally - there are many moments when the formal diploma is required from you. For instance immigration and changing countries. Being an engineer opens a lot of doors, makes it A LOT easier to get a working permit/visa. There are certain types of jobs that require formal education - and without it you will not even be considered a candidate. Right now you are probably young, single and it's not a problem for you to be a contractor and have less stability, but later you'd get married, have children, take a mortgage, and then having a well paid job and organised life in a big corporation is not a bad thing at all.

And moreover catching up with the degree later in life is really difficult.

So, honestly, just finish it. It doesn't have to be spectacular. I've made this mistake, you don't have to.