I have 5 out and about, plus another 3 just bought. They're all still alive after 18 months, 1 hasn't moved since September, but it's up a mountain, so probably wait until spring.
Of the 5 released in the UK, 1 now in US, 1 in Germany, 1 in Switzerland. Until reading this thread, I hadn't realised how well the Germans kept TBs moving - that's my experience too.
None of mine have anything significant attached to them. Maybe that's why they've not gone missing?