Rich Wong, a partner at venture capital firm Accel Partners, doesn’t know if Silicon Valley’s startup boom is at imminent risk of collapse. He does know this: If a founder doesn’t have the stomach to weather a downturn, take the money and run.

“Nobody knows when the windows” to sell are going to close, Wong said. “Now is a very good time to consider all strategic offers.”

While Silicon Valley heatedly debates whether technology valuations have risen to excessive levels, the investors who helped fuel the boom aren’t waiting for an answer. Venture capital firms are starting to take steps to protect themselves in the event of a downturn.  

At Sequoia Capital, an early backer of Apple Inc. and Airbnb Inc., a partner Doug Leone said current valuations aren’t sustainable and that the 43-year-old firm has been walking away from deals that may have been attractive in a different environment. Some VCs are urging their companies to build a rainy day fund to ensure their survival. Even T. Rowe Price Group Inc., the mutual fund company that had been pouring money into late-stage startups, has dialed back its tech investments.

It’s a constant battle deciding whether to invest in a potentially lucrative deal, said Philadelphia financier Rudy Karsan: “Greed versus fear.”

Hand Wringing

Silicon Valley is in the midst of one of its most prosperous periods since the creation of the personal computer. More than $47.3 billion in venture capital investments were made in 2014, the most since the dot-com boom of 2001, according to research firm CB Insights.

There are now 119 startups globally valued at more than $1 billion -- seven of them hitting that mark since June 1, showing there remains no shortage of people optimistic about investing in young technology companies.

The prolonged boom has led to hand wringing about whether increasing valuations constitutes a “bubble” that’s approaching a bursting point. Bill Gurley, general partner at Benchmark Capital Holdings, which has backed companies including Uber Technologies Inc. and Snapchat Inc., has been sounding the alarm for months, arguing that many high-value startups won’t live up to their hype.

Tell-tale signs of a peak are all over -- everyone wants to be a startup investor, including the proverbial doctors and dentists, said Sequoia’s Leone.