1). there are a lot more people who don't reach goal than there are who lose too much weight. Plus if you feel like you're losing too much weight, you can always increase your calories to put the brakes on it - or to start gaining. So I wouldn't worry about this one AT ALL.
2). fewer than 5% of people are able to lose weight and keep it off. You may be one of the lucky ones who can do that - and if so, and you're afraid of the surgery, it's not too late to pull out and try it on your own. I wasn't one of the lucky ones. I spent my first 55 years as overweight or obese. I gained and lost weight a million times and could never keep it off until I had weight loss surgery.
3). hair loss, if you experience it (and not everyone does), is temporary. I lost hair during months 5-8 post-surgery (so...for three months). It wasn't much, though. I could tell because there were more hairs in my combs and brushes, but I really didn't notice it at all when looking in the mirror, so I'm sure no one else noticed it. Plus hair loss after surgery is more like shedding - not huge clumps of loss like one might have after chemo. For a lot of people, they're the only ones who notice it. It's usually more loss of volume than noticeable "bald spots" - and it does grow back.
to me, the risk of losing some hair temporarily vs. being morbidly obese for the rest of my life was a no-brainer. But you may think and decide differently for yourself - and there's nothing wrong with that. If you're not mentally ready for this yet, or want to try on your own to lose weight, then there's nothing wrong with canceling or postponing your surgery. You wouldn't be the first..or last.