So long as assets and liabilities are exchange-rate linked, and payable only in the domestic currency, the central bank still technically has the capacity to serve as lender of last resort in the domestic currency, even without holding massive reserves.
But this  4  The literature uses the concept of a minimum variance portfolio for the economy, which includes a significant share of foreign-currency or foreign-currency denominated assets. BIS Review 126/2006  3  does mean that the impact on the exchange rate of a significant financial crisis is likely to be very large in an economy with extensive dollarization.