No one can guarantee what will happen! When you have the ab separation, it translates to a weak core. How weak of a core depends on how severe your DR is.
The core is the center of our body, and we need to use it every day. Think of using your injured arm, if you are using it despite its injury, you will likely make your arm worse. Same with the core, we have to constantly use it:
Lifting your child up.
Lifting the carseat.
Chasing your toddler.
Getting on and off the floor.
Bending to change the diaper, to bath your baby.
Without a healthy core, you could injure the muscles/tissues/organs that help compensate for the movement, such as your back, spine, intestine, and pelvic floor.
Also, we must address the root cause if you want to have a flat belly (hey, nothing wrong with that even if you are a mom!). Your core can't heal without proper training and techniques. No matter how long you are postpartum, it's never too late to heal, improve and strengthen your core.