So is there a easy way to find out failed cameras ?
I'm only answering because no-one else did. There was a similar discussion in the multi-camera thread. I came up with
this addition to multicam.lua. The lines can be copy&pasted right above the following in multicam.lua:
--[[
return an iterator over selected cams
]]
I have no idea whether it is helpful or not. You can also read the preceding and followup posts in that thread.