No worries, Tero Kinnunen is alive and well! The RIP in the Nightwish videoblog clip was a kind of inside joke which started at the last concert with him with the Nightwish crew, as Aki said above.
Tero has been with Nightwish since the beginning and he is actually the man who had a big part in creating the distictive Nightwish-sound when he recorded the first songs for their demo and later for Angels Fall First -CD at Kitee Youth Center studios back in 1996-1997. Ever since he has been the sound engineer and (co)producer on Nightwish CDs and also travelled as technician and roadie with the band.
During the time he also became well known and appreciated rock/metal studio engineer and producer in Finland, thus he has no lack of work at home. Two years on the road again would have been too much for his current life and work. If you didn't know already, his main job now is running the
E-Major studio owned by him and Emppu Vuorinen of Nightwish.
We will hear his work on several bands' CDs in the future and when Nightwish enters studio for the next CD, Tero will be at the recording desk again.