If you sell it before liquidation, you get the benefit of knowing what you're getting. If you wait until liquidation, you'll get NAV (there's no market price since it's no longer trading). If it's trading at a steep discount, you should, in theory, hold. Due the nature of ETFs, sustained discounts (or premiums) are highly suspect. If there was an arbitrage opportunity, market makers would buy the ETF and sell the underlying narrowing the discount. The fact that it exists could be evidence that the NAV is wrong. Keep in mind, published NAV is based on yesterday's close, like a mutual fund. For ETFs, there's iNAV or IIV, the Intraday Indicative Value. ETF market makers make their own pricing models and as a result, could steer the ETF away from the issuers published IIV. This is common with illiquid underlying symbols.
I would say this depends entirely on the situation. If it's a domestic equity fund, you should be able to get a fair enough market rate. If it's a foreign bond fund, well good luck. For a passive investor, bid/ask spread of the ETF can give an idea of how accurate the market's pricing is. Some ETFs have spreads of $0.01 but only trade a couple times per day. In this case, you could still expect a good price.