Well it's just good to know how the things are working if shit happens. The links given in one of the replies were very helpful. Now I understand the logic.
%% ETFs are very, very unlikely to blow up= ''etf safety'' 500 pages plus of reasons/see also perspectus. An inverse etf can grind down to nothing/ but that is much different. Some of them have the provision they get to report the price 24 hours late/if they want to[which would be a different price from previous trading day...……………………………………………………………..]
There are various kinds of ETFs, you have to research. For example some are 100% physically backed but some are just partially and some are purely synthetic.