I have to preface my answer with a disclaimer. I have never owned one (T120) long enough to see first hand.
That said the question is too subjective for a definitive answer. Just think about all of the factors involved here. Assembly procedure, hone condition, ring type, piston material, ring gap, piston clearance, engine balance, oil brand, and viscosity, areas the bike was ridden, maintenance issues, The list is too long to continue.
Comparing an average among all brands of bikes I have worked on, and known conditions for each of them I would have to say you can get 75 - 85k miles from a cared for engine, and rings. On the other hand you can destroy them in less than 10 miles.
It's a tough question to answer so I'm just going w/ some of the longest lasting engines I have been around.
Honestly nothing can replace putting eyes on the bore, and inspecting the condition. If compression is within 10% of spec., there is no need to open the head. If compression is low, a leakdown test, and the head needs to come off anyway.
As long as you can still see cross hatching, and the cylinder passes the leakdown... no need to pull it apart.
If it is already a high mileage engine, (50-60k engine) and there is no cross hatching... As long as the head is off, go for the gold, and hatch the bores, replace the rings, and do the head work.
I had an '85 Goldwing GL, that rolled in w/ 135k miles. I kept it as a daily driver when my daughter was born, rode it for another 27k miles, and sold it in excellent shape after 2 years.
It all depends on how they were treated, and maintained.