> 1. If I had shorted RUB on US intelligence reports leading up to the invasion, would I be able to collect, or would illiquidity stop me from being able to obtain RUB to cover my shorts?
The keyword you need to put into Mr Google is "B-book".
Unless you:
a) Are a big-cheese in the trading world; or
b) Opened an account with the very very very very small number of brokers that are 100% A-Book
You will almost certainly be trading on a B-book account.
In a simplified nutshell, B-Book means that your order never goes anywhere near the market. Your trades are internalised by your broker, they are market makers for their own book, and they settle their trades internally. Your broker reduces their own internal risk on their B-book by (if necessary) making the necessary risk-reducing trades on the real market.
So in essence, yes you would be able to "collect" because your broker would be doing the settlement internally.
However, and its a BIG however. In exceptionally volatile markets such as Ukraine events, your broker will implement risk management procedures in order to prevent lots of clients blowing up their accounts and therefore exposing your broker to a large aggregated risk. Therefore unless you already had a trade in-play before risk management was enabled, its unlikely you'll be able to put on much now (at least not without a large margin requirement).
I should say that all the foregoing applies soley to "day-trading" (i.e. CFDs, Spread Bets, Futures etc.). For equities ("stocks & shares") then then there is always external settlement.