Power View is not directly part of Power BI, it's a part of Excel.
Anyway, you can build What-if analysis in your Power Pivot/Power BI Desktop model.
An example:
https://javierguillen.wordpress.com/2012/04/22/what-if-analysis-at-the-right-level-of-granularity-in-powerpivot/[/url]
Excel itself has also what-if analysis options. One of those is the Data Mining add-in, which offers what-if scenarios.