I got the opportunity to buy a nice Leica IIIf (incl. Elmar f2.8) that had a CLA in 2010, done by Leica in Austria. I've seen the invoice, both shutter curtains have been replaced and the camera has been adjusted.
Since this CLA has been done in 2010, you think the camera is still ok in 2016? When should I expect to do a new CLA? (if we assume the camera has been treated well in the past years)
I'm sure it's fine, probably for the foreseeable future unless it's abused (dropped in the mud, taken to the beach daily, etc.). Much of a CLA is about removing old lubricants and replacing them; modern lubricants are very stable and long-lasting, so they should be fine for a very long time. Done properly, as I would expect given the source, adjustments on these cameras hold very well.
After having an accident with my M3 a few years ago (I'd broken the glass on the front of the viewfinder) Leitz said they'd do the repair but it would need a CLA. What an honest company they changed the cracked glass and said the camera had been serviced quite recently and didn't need a CLA they had tested the shutter speeds, so charged me a lot less than the estimate.
Leitz officially stopped repairing pre-M series cameras quite a few years ago, but then they use Malcolm Taylor here in the UK to do all their restorations & repairs
I wish I had bought a NEW IIIf + 50mm f3.5 Elmar in Iserlohn, Germany in the Canadian Maple Leaf store for £ 45 - 00 !!! It was 1957 and I was there in the British Army but I was paying off a Zeiss Contax III + 50mm f1.5 un-coated Sonnar I had got when I was in Berlin -- so could not afford TWO 35mm cameras.
If it was used fairly regularly and not dropped likely fine. If it sat unused in a open box in a musty/moist garage, cellar or attic for 5 years then no.
My Zeiss Contax III was 'well used' -- it cost £ 38-00 in British Pounds after changing from German D. Marks when we got 11.5 D. Marks to one British pound. I was in Berlin in the British Military Hospital Spandau near the Russian Zone border. I was a Path Lab Techician -- there used to be a German Camera Dealer visit every week and he had a Leica III with 50mm f2 Summitar all scratched or the Contax which I chose. I didn't know much about 35mm cameras at the time. £ 38-00 was a lot of money on British Army Pay and I had to pay it off monthly. I took some good photos in the Russian Sector War Memorial gardens with it on an organised trip on 'Perutz Peromnia 21DIN film'