The technicality aside, you could "ban" it. You may not be able to stop it, because people could use satellites to get internet from other places, there are global companies that offer horrible bandwidth and speed, but it is there. But that is not about banning, that is about stopping. So if Russia bans it, then they can, and people could either stop, or they could try to find alternatives.
On the other hand, they can't really afford to get out of international internet, because that would put even further economical problems to them on top of the current ones that they have, which is why I doubt it would happen anyway, it would probably not happen.
Even if you ban it, people would be able to use VPN to overcome that so they know this, they have tried to limit the way Russians use internet before, and they have limit what type of freedoms Russians will get, and they always fail because internet is just way too free to be limited. You could even do bad things online nowadays in the darknet, hopefully nobody ever uses that again but it's there, it's usable and it's not cool at all.
In the end, crypto is a lot like that, they are not saying they will cut themselves out of global internet neither, the fact that they "act" like it is just a way to scare people but in the end they know they can't, and that is why they won't.