1. No Jio does not offer static ipv6.
2. It would if your internet is disconnected or your
router is rebooted etc, usually Ipv6 is given based on prefix delegation guess that's a bit helpful.
3. /64 is a very big range, you won't really run out of ips, plus that /64 will be shared with other customers.
PS - there are still many apps that do not support Ipv6 completely or natively. A lot of ISPs that also do offer Ipv6 comes with a fked up Ipv6 config, that disconnects every couple of hours. There are still millions of websites and websockets that you can't access without an ipv4. So yeah, unless it's adopted widely, don't talk about how smart you are with your Ipv6 or how much gravy you use with your Ipv6. For a new user, Ipv6 is still difficult to deal with.