Site down after upgrading Views
I don't think there is really a "100% Safe" solution for upgrading your modules. But for the future, the best thing that you can probably do is:


Make sure that you are using a version control system such as CVS, SVN, Git, etc. That way when you update and see that things go south you can always revert your changes.
Always backup the database before running update.php. Again, if things don't work out, you always have a restore point.
It is a good practice to read the release notes of the version that you are upgrading to and to take a peek at the issue queue of the module in question. Most likely another Drupal developer would have tried already to perform the same update that you are trying to perform, and there is an entry in the issue queue indicating what was the problem when updating. Sometimes if there's an entry in the issue queue it will also tell you how to upgrade from one version to another. Sometimes you can upgrade without no problems, sometimes you can't, and other times you have to follow a few manual steps before upgrading.


As for the present tense, since you already attempted the upgrade, I would start by following step #3 above, and if you can't locate a relevant entry in the Views issue queue that points you in the right direction, you're more than welcome to open one.