We're in the case of the game Lego Indiana Jones for our son.
We have a PS4 and unfortunately there's the game only for the 3.
Now I found it at PS Now. But now every month to pay 10 euro for PS now + 10, - euro PS Plus only for a game, not really worth it. What happens if I download a game there and eventually quit? Can I still play it offline or not?
When you buy a game on PSN, it is yours. Then you can also play it offline and do not need a subscription.
If you only lend the game, be it through PSNow or PS +, it will be yours for the subscription period. If you quit, you will not be able to access it.
By the way, PS + only costs 60 euro once a year instead of having to pay 12 x 10 euro a month.