Hey, I'm also relatively new to the forum so take my opinion with a grain of salt!
However as I intend to keep my B9 for many years to come I've also researched this quite a lot but I will be more use in maintenance rather than reliability!
Regular maintenance wise I would imagine the Cambelt and Water pump will need changed if they have not done so already, however I would've expected it to be done because anyone leaving it on for 115k miles either couldn't care less or has some serious faith so I would definitely look into that.
I also am aware that the DPF system is supposed to be inspected at regular intervals around this point (115k miles) and further 20k intervals for inspection of function.
Reliability wise the 2.0tdi is supposed to be a pretty solid engine and depending on what type of oil changes it's been on, I would expect a bare minimum of 150k+ miles from this car without many problems.
Good luck, keep us updated!