Hi -
I'm not sure what version of InfoPath you are using or if you are using browser or filler forms.
However, in all instances, moving, renaming, or deleting a form field will cause XML opened with the modified template to lose data if the template is set to upgrade existing XML. Mind you - the old XML generally won't open with the modified template unless you've set the template to upgrade existing XML. You can add custom upgrade code, if you like, to handle for this. In my opinion, it is better to simply refrain from moving, deleting or renaming nodes in a production template.
In IP 2010, I think the options for versioning are little more granular - at least where filler forms are concerned. The form template is cached on the user's machine, and in 2010, you have more options as to whether or not that cached template should be updated - these are under Form Options / Versioning.
This article on Office Online, while written for IP 2007, seems to be a good overview.