I think you've hit the nail on the head. Scrooge is a lone prospector who's just gotten very lucky with the help of an obscure legal ruling and a lot of support from a wealthy patron who happens to have taken a shine to him as he passes through. 

If he leaves the country, there won't be anyone to support his claim (noting that it's based on him **occupying the land continuously**) or file his paperwork in court and although he nominally owns a valuable asset, in reality it's going to be hard for him to borrow against it in order to hire any kind of legal support, plus he needs to leave urgently. 

Better to take the cash offer than try to fight it out from afar.