I'd argue that in this case the centralization helps because blocking GCM would kill all notifications for all apps. As long as they (Russia) are not willing to do that Telegram can use this as a side-channel to update their IPs for all clients.
The other option would be for google to turn push notifications off selectively for Telegram and only in russia. Not sure if they can/will do that.
If Google will comply with an order to remove apps from the store in certain regions then they can certainly comply with orders to filter push messages destined for specific apps as well.
My problem with GCM is not the implementation on the client, but the fact that Google sees traffic. I don't want Google to see my data nor my metadata.
I always get notifications about Telegram messages on my phone at around the same time (within a second or so) as I get the notification on the web client.
Currently Telegram keep working because it's get new backend IPs constantly via Google Play / AppStore services. Since push notifications are centralized they'll stop working as soon as application removed from stores so app wouldn't be able to get lists of unbanned IPs.