I've worked at a lot of for profit business (not banks though, i can understand that in those kind of business requirements are diferrent) and made live databas

I've worked at a lot of for profit business (not banks though, i can understand that in those kind of business requirements are diferrent) and made live database updates in all of them. In 99% of the cases all goes well and in the remaining 1% you need to revert to your backup (always make backups before doing anything!) and have a couple of minutes of downtime. It really depends on what kind of business you're in whether this is acceptable or not.