There is no way they can afford to fragment the internet. They need open source libraries, they need access to information, they need access to education, etc. If they do that they will gp backward economically.
You can unfortunately retain a lot of the utility of the internet while simultaneously sucking out the ability for it to be effectively used for political activity if you're willing to build the infrastructure required.
I think it's rather the opposite. Why do you think tencent, alibaba, etc., exist in China, instead of the US alternatives? It's simply because there was a wall in place. Honestly, I'm not sure why more large countries aren't doing this - it's an easy way to build your own digital industry up.
It would be wise for someone in the Russian government to say "You will end up shining the shoes of the Chinese!" a la Italo Balbo at this point.
In addition, I'm sure there's enough tech skill and manpower in Russia to create most any web service given enough incentive.
More than 17 millions of IP addresses were blocked in 2018 [1][2] including large segments of Google/Amazon/Azure/DO/Linode etc. Although recently roskomnadzor unblocked most of them (perhaps due to the spread of DPI among internet providers, so they able to deal with https now and act more accurately), but ~800,000 IPs remains blocked. The government doesn't give a shit about creating a bad reputation for online business in Russia. Instead, actively engaged in "import substitution", e.g. making Сhina-like isolated payment card system [3] or spending millions for "national search engine" [4] (currently bankrupt, AFAIK). They are seems to be totally OK with isolation.
[1] https://www.theguardian.com/world/2018/apr/17/russia-blocks-...
[2] https://en.wikipedia.org/wiki/List_of_websites_blocked_in_Ru...
And will be monitored. I've read speculation that some of the popular VPNs that still function reliably in China are likely to be government-controlled.
From an authoritarian's controlling standpoint, it makes sense to deliberately provide some "outlets" to trap the unsophisticated people who want to escape your control. Out of the pan an into the fire, so to speak.