The acquiring company can always just give them bonuses irrespective of the acquisition.
Of course. But the acquirer usually has no incentive to line the pockets of the investors, so they'd rather lower the price by spending the M&A nut on the team instead.
It's usually among the first things to go in a negotiation.
Liquidation prefs are rarely exercised, at least when the acquirer is clueful. (The company spending the money wants the incoming employees to be reasonably incentivized, often that takes the form some delayed payout. They really don't care if the investors make their money back or not.)