In the data set I used for reference, Series C+ companies still mostly failed to exit. Even at the furthest extreme the data tracked, of the 35 Silicon Valley companies that raised a fifth round 18 failed to exit or raise more money.
On the other hand, there are some advantages that may make later companies less risky: the timeline to exit may be shorter (though that is less true in the case of an early M&A, which ~23% of the cohort found). The nature of the risks may change in ways that make it easier to evaluate. And cash salaries usually rise in the later stages, reducing the marginal cost to employees.
There was no stage at which venture-backed companies stopped being a risk, but that's also true of public companies that grant options: it is always possible that the share price goes down and the options are worth nothing. I think the takeaway is that in this 2006-2008 cohort, earlier startups were less at risk of running out of money that most people would assume.