Do they even have to borrow money, they could just print their shit tokens out of this air and use it to buy assets to 'prove' that their reserves covers all liabilities.
Exactly. It's happened many times before. An exchanges goes bankrupt because of their own shady practices or because of a hack, so they either launch a shitcoin and "pay" back their users in this worthless shitcoin instead of bitcoin, or they just print a few hundred million of an existing shitcoin out of nothing to keep themselves solvent. A prime example of this is Bitfinex and Tether, where they printed almost a billion USDT out of nothing and gave it to themselves after they were hacked and insolvent.
My most recent favorite snippet from the trial below. Gary Wang was a the CTO of FTX and co-founder alongside SBF:
Lawyer: Are you aware of the difference between solvency and liquidity?
Gary Wang: Now I am.
What an absolute clown show.