So are there any other gacha games that ended its natural lifetime and shut down?
Have you heard of the works of the magical company square enix?
In general: Fuck you, we got the money. When the servers down, you lose it all. Even if you bought minutes before the reset ends, as far as they're usually concerned it's no problem. Your only way of getting it back is charging back through some other source, in the end. A lot don't even run any real 'whoops everything is fucking busted, go nuts with all these free resources'. It's just... gone.
It sucks, but it's honestly kind of the risk you often run and with games like puzzle and dragons atleast you've honestly atleast had years of playtime to put into it.
Imagine if it was a fresh hopeful game that just couldn't pan out for the company.