Most Helpful Guy
There is no stock answer, it depends on you, on them and on whether or not being friends will likely cause any complications, confusion or delay in closure. If you had a good break up in which neither of you hold desires to be back together then you could probably be acquaintances or even friends. If one of you is still holding desire to reignite the relationship then it is probably best that you don't stay in touch, at least for a while.
Most Helpful Girl
I don't see a problem with it tbh. I'm still friends with my ex and my boyfriend is friends with his ex. As long as it's nothing or ever going to be more than friends then it's fine.