If they are not checking their email and they are not following their social channels, then there's no way to reach these members who are inactive, if they still have large funds here and BETBTC cannot contact them, then they cannot blame BetBTC anymore if they cannot withdraw their funds anymore, always check your inbox and follow sites where you have funds.
That's on them if they don't check their emails but the site still has the responsibility to at least reach out to them in about 3 months at the least so they can't be seen as someone that has took advantage that their clients didn't reply because it's still their clients money after all, you don't want that to happen to you right? Then don't do it to others and karma will bless you.
I'm sure if they see some big money still not withdraw that time, they cannot just forfeit it if they are regulated, but if that's their rules, then those clients that were not able to read the announcement could still go after them, but let's just not think of that, that's only the worst-case scenario, BETBTC maintain their good reputation from the start to finish, so I hope they'll exit cleanly.
BetBTC if they are planning to scam this money, it would be easy for them to go and runaway,
But they are not doing it as they wanted to go cleanly. They value their business and with how they
are communicating and giving the time for all the gamblers who have active balance, they are open to communication.
so in-case that there's still some that still haven't withdrawn their money
communicating to support thru emails or here might help them.