The liquidity crunch in the global market can be used to negotiate a better deal for Saudi Arabia. Still, it's hard to know how good it will be without knowing more details.
Hard for me to say, a lot stuff is traded over the counter, and one can get short exposure alot of different ways. Blackrock[0] has about $10 trillion notional for the single name cds market in 2016, estimated in 2017 that there was about ~$15,000 million avg daily volume in HY, and ~$26,000 million in IG (cash traded bonds, etfs, and cdx) and that's not considering the notional on the derivatives (swaps/options) on those.
By comparison, Saudi Arabia produces 12 million barrels of oil a day: if the price drops $30 they need to make $360 million per day to cover that, or $30 billion if they carried out the trade over a three-month period.
If the total single-name CDS market is $10t and $1t of that is in oil and gas firms...it doesn't seem out of the question you could get a $30b position. Not that I really believe this is what's going on.
Yeah, for all we know they could have loaded up on CDS on O&G plays and stand to offset any losses just by triggering default clauses on the frackers.