A perpetual is a contract with the exchange, not with another trader directly. Your profit exists because the venue says it does and can be withdrawn because the venue permits it. That is a counterparty relationship, and it is unavoidable.
Where the shortfall goes
When a liquidation fills worse than bankruptcy price, someone eats the difference. The insurance fund absorbs it first, and auto-deleveraging closes profitable positions second. On the venues that still use it, the third layer is socialised loss: the shortfall is charged across profitable accounts directly.
All three mean the same uncomfortable thing. In an extreme move, the money you have made is not entirely yours until you have withdrawn it, because the mechanism keeping the book balanced can reach into it.
Beyond the balance-sheet mechanics
Venue risk is broader than the liquidation engine. An outage during a violent move stops you managing a position while the mark keeps moving. Withdrawal suspensions freeze a balance that is nominally yours. Neither shows up in anything you can chart.
And these correlate with exactly the conditions where you most need access: outages cluster in the same volatility that triggers cascades, so the failure arrives when the position needs attention most.
What can actually be done
Not much cleverness, mostly discipline. Do not hold more on a venue than you would accept losing entirely. Split across venues if size warrants it — which has the side benefit of making the per-venue funding differences a cost you can arbitrage rather than merely observe. Withdraw profits rather than compounding them in place indefinitely.
The reason to state this plainly is that it is the one risk in this whole series that position sizing does not solve. Sizing protects you from the market. It does not protect you from the place you are trading.