It would be challenging. Besides ego, they might not feel the passion and connection they most likely had with their own startup, loss of control in ownership and decision making can be hurtful.
But, it all comes down to mindset and willpower. If the person wants to rejoin 9-5 workforce with a mindset that he/she is accepting defeat, anything and everything around would feel offensive (even if others didn’t intend it that way) and mundane.
If taken in a positive spirit, one can learn from experience and either take a break temporarily and bounce back or to share one’s expertise with another awesome company and being valuable part of it.
Interviewers in this case are likely to judge the candidate based on his/her past achievements, social image and professional network all put together. (Eg: Say the person has an elite educational background like IIT, IIM etc, they won’t be quick to judge because there is a presumption of excellence. On the other hand, if it’s a grad student with a normal college degree who founded his company and it crashed shortly, in this case he/she might be judged massively.)
Regardless, all that matters is how one introduces oneself, skill set that he/she offers to the new company and makes the best but honest narrative of unfortunate experiences.