So your domain, blabla.com, has two nameservers, as you expressed above. Those are ns1.bubu.net and ns2.bubu.net.
If you aren’t the one hosting ns1.bubu.net and ns2.bubu.net… if those aren’t nameservers running on your Virtualmin server that you manage – then you don’t want Virtualmin’s DNS feature enabled.
Virtualmin’s DNS feature means “Hey, I’m hosting DNS for this domain”.
But it sounds like in your case, you aren’t. DNS for your domain is hosted over at bubu.net.
What DNS does is provide a way for browsers to get your server’s IP address when someone browses to blabla.com.
Since that IP address is being given out by ns1.bubu.net and ns2.bubu.net, the only thing running the DNS feature on your server will do is cause trouble
Now, you asked, “will disabling DNS cause the content of your site to be offline?”
When you stopped the BIND service, did your web content still work?
Disabling the DNS feature simply removes the blabla.com zone from your DNS server… which is certainly no worse than turning off the daemon
So if ns1.bubu.net and ns2.bubu.net are DNS servers hosted at some other site, I really would recommend going into Edit Virtual Server for blabla.com, and disabling the DNS feature – it’s not actually doing anything.
You can always re-enable it afterwards if you don’t like the results
And if you’re really worried, just do a full backup of your Virtual Server before making any changes (though, of course, you should be making backups for your Virtual Servers every night