Xbox game pass, only play during subscription?

So,

Dragonball xenoverse 2 is down in the Microsoft Store and if I buy it something remains.

Now I ask myself: during the xbox game pass subscription, do you keep the titles forever or do they only run during the subscription?

And can I then play online?

When the gamepass has expired you can no longer play the games, you can keep the games that you have bought at a reduced price. You can only play online if you have the gamepass ultimate.

Or Xbox Live Gold. Gamepass Ultimate is only a combination subscription of Xbox Live Gold and Xbox Gamepass.