How does that usually work?
In general I think acquihires are moderate successes for the founders. Not just financially but external validation of their collective skills as a team.
I bet the investors get their money back, the founders of Cover get $2m - $4m each in stock alone (vesting over 4 years of course), and the employees get $500k / year in total comp.
The $1.7M investment was a seed round (in Oct 2013), with lots of individuals putting money in[1]. If it were bought for say $20M (who knows?) then I'm pretty sure those seed investors would be happy with their 5x to 10x returns (depending on liquidation preferences) in 6 months.
If it were bought for $5M, then not so much. But if it was only $5M on the table I doubt they would have sold that quickly.