Static IP Adresses
Both the IPv4 address and the IPv6 /64 prefix assigned to your VPS are "static".
This means that they will not change for as long as you have the virtual server.
The IP addresses also remain unchanged in case you need to reinstall your KVM virtual server, no matter how long the reinstall will take you.
Bottomline: An IP address assigned to your VPS remains yours till you cancel your server.