The Persistent chat role has been removed in Skype for Business 2019 along with code hence you will not be able to see the Persistent chat role object in topology.
Refer to this
article
If you are looking for Similar feature, Skype for Business 2019 have streamlined the Teams migration you shall go for it.
Refer to this
article
Any way not to worry, as the Skype for Business 2019 can co-ex with Skype for Business 2015 Frontend and Persistent chat servers and everything works as expected for the users who are hosted in Skype for Business 2019.
Basically the accounts which are hosted in SfB 2019 will leverage SfB 2015 Front end to get the PChat functionality.
**Mark as Answered if this information helps, as it might help other if they have similar concern**
Best regards, Neeranjan