How often do Officers leave the military as O-2s?

Lt you have to do what's best for you and your family. Sounds like you don't have plans to make it a career so know you've served your country. That's more than most can say.

Was it worth it?

There’s no perfect time to pick whether to stay or go. 4 years or 40; unless you’re a General, you will likely be asked to leave, especially if on active duty. So go when you feel you won’t regret making a long-term decision based on short-term thinking. If you’ve hit all your career goals, time to go.

Active. Yes. Bad. Real real bad

I've known quite a few officers who had short Active Duty Service Obligations (ADSO's), who left active duty as 1LT's after three years and went to the USAR or ARNG afterward. I also knew a few who left active duty as 1LT's after getting in trouble; one lost his M-16 in the field (it was later recovered), another missed movement for a deployment and had to deploy late, traveling with another unit; another got a GOMOR because she had an affair with a married male officer. I even knew one prior service Infantry 2LT with a wife and three kids who got booted out because he was constantly late for formations. The one who lost his weapon and the one who missed movement were given a second chance in the USAR, and actually did very well; I don't know what happened with the others.

I only know one Reserve Component officer who got out as a 2LT, simply because he wanted to be commissioned on active duty but didn't get it. He completed OBC, but then resigned. He was also a prior service guy. He went into a civilian career where he never mentioned his commissioned service; as far as his employer is concerned, he's a former Regular Army NCO.

In your case, I'd recommend taking the promotion to Captain if you're promotable in the ARNG. Nobody questions the service of an officer who gets out as a Captain, whether that officer is AC or RC; however, if you get out of the ARNG as a 1LT, it might raise a few eyebrows. Sure, you can explain it as a personal preference and show people your good OER's, but that's going to get really old after a while. Also, you never know ... you might really enjoy serving as a Company Commander.