As reliable as probably any 30 year old vehicle. If that's the actual mileage, your drive train should have a lot of life left. But you still need to plan on replacing old rubber and plastic parts, etc. Also, it obviously has spent a lot of its life sitting which is not good for a car. 

If it runs and drives, you're doing well at that age. I wouldn't daily drive it even though the miles are low just because who knows what may happen once a car gets that old. But as a knock around car or weekend grocery getter, I'd say it will be good.

There's not enough information. How long has it been sitting? For example, let's take the fuel tank. Has it been empty, or has fuel been spoiling, for years, corroding the tank?

When was it last taken out on the road? What is the condition of a 30 year old suspension, radiator, engine, after all these years, especially if it has been sitting? And sitting, where? Outdoors, in a heated garage, in a barn? What's the condition of the transmission fluid, after all this time? (This is assuming that it's been sitting).

When was the oil last changed? When were the seals changed? How are the belts and hoses after 30 years? And so forth. What is the damage that time and space hath wroth, so to speak?

There's no way to know your antique car's reliability (anything over 25 years is legally an antique) without knowing those details.