Yeah, it’s tough to say. Company wasn’t distressed, but it “only” 2x’d over 8+ years. Pretty much a classic flat/no growth situation with modest profitability.
It wouldn't have to be a PE buyout for equity to be zeroed out. Any buyout could lead to this, even in a non-distressed company (as pointed out by another poster).
Source: Me w/options in two startups that were acquired by public companies.