I have a Toyota T-100 that I have had for about six months and it has about 211,500 miles on it, with no major replacements or accidents and all original parts, but I am nervous that it may not last too much longer. Around what mileage will it start to break down or will it maintain it self if I keep up with its routine check ups?

At 211k miles it probably has had most of the parts that break down replaced already. The main engine components are good for 300k + if it was maintained correctly. If the transmission hasnt been replaced it is probably on its last legs and a very expensive repair.