Leave the paint alone and just ride it.

There's no percentage in looking, since you're not likely to gain any useful info. It's either cracked (doubtful) or not. It'll either last many years or it won't. Either way the worst that can happen is that the crack (if any) propagates and the chain stay eventually fails.

Since any effort to repair it or prevent failure is as expensive and complicated as repairing it after it fails, you might as well wait to cross that bridge until (if) you come to it. There's no danger to riding it this way, since the crack will propagate and become visible long before it fails. Even if it somehow fails without warning, chainstay failure rarely (if ever) leads to a crash.

In short, you have nothing to lose by leaving it alone, and nothing to gain by making it cosmetically worse.

I'd make up a good story about how you were jumped by three big guys, and you used the bike to protect yourself when one swung a 2x4 at your head. the bike took one for the team and saved you before you were able to jump on and sprint away.