The cantonal banks in Switzerland can not go bankrupt without the state going bankrupt as well. That called state guarantee here.
In practice a lot of other banks seem to have non-formal state guarantees as well, because they‘re bailed-out.
Regarding securities:
There‘s just a legal order in which creditors are refunded during bankruptcies. Biggest creditors first. So Blackrock will probalby get back their securities but not you.