Segues will not run on IOS 4 now what?
Actually the concept of segues was introduced first in iOS5, however it is also stated in the library documentation.

Nevertheless, you can try to create standalone nib files and copy your UI*ViewControls from the storyboard into the nib file(s). Of course you are still not allowed to use segues but you can easily reintroduce IBActions to handle transitions between the views. It's still some effort to migrate, but not an impossible mission.

In order to avoid such a situation, I would suggest you to make a short requirement analysis (functional as well as non functional) before coding.