It will all be in the End User Licence Agreement that you consented to when you "purchased" your copy of Trainz.
Actually, you did not purchase it in the same sense that you would when purchasing a car, a Mars Bar, a computer - all you have purchased is the right to use (a licence in other words) the software that is always owned by N3V. Legally, they can require you to uninstall it at any time. The small print in the licence (you did read the small print didn't you?) will prevent you from transferring your software licence and the software to anyone else - so they cannot then use it and your licence.
I hope that makes it clearer.