Unfortunately pianos greatly decline in value with age. If it's in really, really good condition, with good sound, responsive keys and all that good stuff you can possibly get more than zero dollars for it. For old pianos that are not in good condition the deal can often be "you get it for free if you can arrange transporting it away from here".
Do you think there would be value in getting an official appraisal? My assumption is that it would be useful to have both to potentially sell (again if anyone would even pay for it), and to store (for insurance). I guess they could also tell me if it will likely be in good condition to play in the coming years as well?