It is impossible to know because none of us can predict the future. But the nature of relationships depends in great part on direct contact, so it would not be too much of a leap to say that living at such a great distance apart would not help the relationship because it will interfere with frequent contact. My own opinion is that courts should be very reluctant to approve such plans to relocate because the impact on the relationship with the non-custodial parent can be signifcant.
Don't let her, if you can. Get all the help yo can to get her to stay. Children need their father as much as they need their mother. If anything, she should move closer to you (less than 45 minutes) so that you can see them more often. If you are a good dad, love them, support them and help them, they need you in their lives. Good luck.