Heading towards CIS-2020.

Why wouldn't the hotel in St. Petersburg refund the money? They are obligated to return it if you demand it right now.
Regarding the airline tickets - which airline is it?

Kirill, resorts, sanatoriums, and recreation centers are closed until June 1st, if anything. Throughout Russia (in the regions, they are still trying to force a square peg into a round hole, as the wording of the government decree allows for various interpretations, but the final result will be the same - everything is closed).
Last night, they started evicting everyone from hotels in Sochi.

Postponing the CIS summit to August (or later) is no longer just a guess or a backup plan, but the only possible option in these circumstances. Therefore, reschedule your booking and ticket dates to August if you plan to go.
Getting a refund is more complicated, but it can be done: get a sick leave certificate and receive a full refund.

P.S. I am amazed by the naivety and stupidity of our citizens. I myself will not go out, not even to St. Petersburg, but a bunch of idiots rushed off on trips to visit relatives and friends for barbecues and other things (spreading the infection to all regions).